Complete inhibition of intimal hyperplasia by perivascular delivery of paclitaxel in balloon-injured rat carotid arteries

Highly flexible and porous silk fibroin microneedle wraps for perivascular drug delivery

Various perivascular drug delivery techniques have been demonstrated for localized post-treatment of intimal hyperplasia: a vascular inflammatory response caused by endothelial damages. Although most perivascular devices have focused on controlling the delivery duration of anti-proliferation drug, the confined and unidirectional delivery of the drug to the target tissue has become increasingly important. In addition, careful attention should also be paid to the luminal stability and the adequate exchange of vascular protein or cell between the blood vessel and extravascular tissue to avoid any side effect from the long-term application of any perivascular device. Here, a highly flexible and porous silk fibroin microneedle wrap (Silk MN wrap) is proposed to directly inject antiproliferative drug to the anastomosis sites while ensuring sufficient vascular exchanges. Drug-embedded silk MNs were transfer-molded on a highly flexible and porous silk wrap. The enhanced cell compatibility, molecular permeability, and flexibility of silk MN wrap guaranteed the structural integrity of blood vessels. Silk wrap successfully supported the silk MNs and induced multiple MN penetration to the target tissue. Over 28 days, silk MN wrap significantly inhibited intimal hyperplasia with a 62.1% reduction in neointimal formation.

Deficiency of peroxisome proliferator-activated receptor α attenuates apoptosis and promotes migration of vascular smooth muscle cells

Peroxisome proliferator-activated receptor (PPAR) α is widely expressed in the vasculature and has pleiotropic and lipid-lowering independent effects, but its role in the growth and function of vascular smooth muscle cells (VSMCs) during vascular pathophysiology is still unclear. Herein, VSMC-specific PPARα-deficient mice (Ppara ^ΔSMC) were generated by Cre-LoxP site-specific recombinase technology and VSMCs were isolated from mice aorta. PPARα deficiency attenuated VSMC apoptosis induced by angiotensin (Ang) II and hydrogen peroxide, and increased the migration of Ang II-challenged cells.

Truncated YY1 interacts with BASP1 through a 339KLK341 motif in YY1 and suppresses vascular smooth muscle cell growth and intimal hyperplasia after vascular injury

AIMS

In-stent restenosis and late stent thrombosis are complications associated with the use of metallic and drug-coated stents. Strategies that inhibit vascular smooth muscle cell (SMC) proliferation without affecting endothelial cell (EC) growth would be helpful in reducing complications arising from percutaneous interventions. Our group previously showed that the forced expression of the injury-inducible zinc finger (ZNF) transcription factor, yin yang-1 (YY1) comprising 414 residues inhibits neointima formation in carotid arteries of rabbits and rats. YY1 inhibits SMC proliferation without affecting EC growth. Identifying a shorter version of YY1 retaining cell-selective inhibition would make it more amenable for potential use as a gene therapeutic agent.

METHODS AND RESULTS

We dissected YY1 into a range of shorter fragments (YY1A-D, YY1Δ) and found that the first two ZNFs in YY1 (construct YY1B, spanning 52 residues) repressed SMC proliferation. Receptor Binding Domain analysis predicts a three residue (339KLK341) interaction domain. Mutation of 339KLK341 to 339AAA341 in YY1B (called YY1Bm) abrogated YY1B's ability to inhibit SMC but not EC proliferation and migration. Incubation of recombinant GST-YY1B and GST-YY1Bm with SMC lysates followed by precipitation with glutathione-agarose beads and mass spectrometric analysis identified a novel interaction between YY1B and BASP1. Overexpression of BASP1, like YY1, inhibited SMC but not EC proliferation and migration. BASP1 siRNA partially rescued SMC from growth inhibition by YY1B. In the rat carotid balloon injury model, adenoviral overexpression of YY1B, like full-length YY1, reduced neointima formation, whereas YY1Bm had no such effect. CD31 immunostaining suggested YY1B could increase re-endothelialization in a 339KLK341-dependent manner.

CONCLUSIONS

These studies identify a truncated form of YY1 (YY1B) that can interact with BASP1 and inhibits SMC proliferation, migration and intimal hyperplasia after balloon injury of rat carotid arteries as effectively as full length YY1. We demonstrate the therapeutic potential of YY1B in vascular proliferative disease.

Myostatin Inhibits Vascular Smooth Muscle Cell Proliferation and Local 14q32 microRNA Expression, But Not Systemic Inflammation or Restenosis

Myostatin is a negative regulator of muscle cell growth and proliferation. Furthermore, myostatin directly affects the expression of 14q32 microRNAs by binding the 14q32 locus. Direct inhibition of 14q32 microRNA miR-495-3p decreased postinterventional restenosis via inhibition of both vascular smooth muscle cell (VSMC) proliferation and local inflammation. Here, we aimed to investigate the effects of myostatin in a mouse model for postinterventional restenosis. In VSMCs in vitro, myostatin led to the dose-specific downregulation of 14q32 microRNAs miR-433-3p, miR-494-3p, and miR-495-3p. VSMC proliferation was inhibited, where cell migration and viability remained unaffected. In a murine postinterventional restenosis model, myostatin infusion did not decrease restenosis, neointimal area, or lumen stenosis. Myostatin inhibited expression of both proliferation marker PCNA and of 14q32 microRNAs miR-433-3p, miR-494-3p, and miR-495-3p dose-specifically in cuffed femoral arteries. However, 14q32 microRNA expression remained unaffected in macrophages and macrophage activation as well as macrophage influx into lesions were not decreased. In conclusion, myostatin did not affect postinterventional restenosis. Although myostatin inhibits 14q32 microRNA expression and proliferation in VSMCs, myostatin had no effect on macrophage activation and infiltration. Our findings underline that restenosis is driven by both VSMC proliferation and local inflammation. Targeting only one of these components is insufficient to prevent restenosis.

Design and Characterization of Injectable Poly(Lactic-Co-Glycolic Acid) Pastes for Sustained and Local Drug Release

PURPOSE

We describe the preparation of injectable polymeric paste (IPP) formulations for local and sustained release of drugs. Furthermore, we include the characterization and possible applications of such pastes. Particular attention is paid to characteristics relevant to the successful clinical formulation development, such as viscosity, injectability, degradation, drug release, sterilization, stability performance and pharmacokinetics.

METHODS

Paste injectability was characterized using measured viscosity and the Hagen-Poiseuille equation to determine injection forces. Drug degradation, release and formulation stability experiments were performed in vitro and drug levels were quantified using HPLC-UV methods. Pharmacokinetic evaluation of sustained-release lidocaine IPPs used five groups of six rats receiving increasing doses subcutaneously. An anti-cancer formulation was evaluated in a subcutaneous tumor xenograft mouse model.

RESULTS

The viscosity and injectability of IPPs could be controlled by changing the polymeric composition. IPPs demonstrated good long-term stability and tunable drug-release with low systemic exposure in vivo in rats. Preliminary data in a subcutaneous tumor model points to a sustained anticancer effect.

CONCLUSIONS

These IPPs are tunable platforms for local and sustained delivery of drugs and have potential for further clinical development to treat a number of diseases.

Non-transdermal microneedles for advanced drug delivery

Microneedles (MNs) have been used to deliver drugs for over two decades. These platforms have been proven to increase transdermal drug delivery efficiency dramatically by penetrating restrictive tissue barriers in a minimally invasive manner. While much of the early development of MNs focused on transdermal drug delivery, this technology can be applied to a variety of other non-transdermal biomedical applications. Several variations, such as multi-layer or hollow MNs, have been developed to cater to the needs of specific applications. The heterogeneity in the design of MNs has demanded similar variety in their fabrication methods; the most common methods include micromolding and drawing lithography. Numerous materials have been explored for MN fabrication which range from biocompatible ceramics and metals to natural and synthetic biodegradable polymers. Recent advances in MN engineering have diversified MNs to include unique shapes, materials, and mechanical properties that can be tailored for organ-specific applications. In this review, we discuss the design and creation of modern MNs that aim to surpass the biological barriers of non-transdermal drug delivery in ocular, vascular, oral, and mucosal tissue.

Effects of paclitaxel intervention on pulmonary vascular remodeling in rats with pulmonary hypertension

The aim of the present study was to investigate the effects of paclitaxel (PTX), at a non-cytotoxic concentration, on pulmonary vascular remodeling (PVR) in rats with pulmonary hypertension (PAH), and to explore the mechanisms underlying the PTX-mediated reversal of PVR in PAH. A total of 36 rats were divided into control group (n=12), model group (n=12) receiving a subcutaneous injection of monocrotaline (60 mg/kg) in the back on day 7 following left pneumonectomy and PTX group (n=12) with PTX (2 mg/kg) injection via the caudal vein 3 weeks following establishing the model. The degree of PVR among all groups, as well as the expression levels of Ki67, p27^Kip1 and cyclin B1, were compared. The mean pulmonary artery pressure, right ventricular hypertrophy index [right ventricle/(left ventricle + septum) ratio] and the thickness of the pulmonary arterial tunica media in the model group were 58.34±2.01 mmHg, 0.64±0.046 and 65.3±3.3%, respectively, which were significantly higher when compared with 23.30±1.14 mmHg, 0.32±0.028 and 16.2±1.3% in the control group, respectively (P<0.01). The mean pulmonary artery pressure, right ventricular hypertrophy index and thickness of the pulmonary arterial tunica media in the PTX group were 42.35±1.53 mmHg, 0.44±0.029 and 40.5±2.6%, respectively, which were significantly lower when compared with the model group (P<0.01). Compared with the control group, the expression levels of Ki67 and cyclin B1 in the model group were significantly increased (P<0.01), while p27^Kip1 expression was significantly reduced (P<0.01). Following PTX intervention, the expression levels of Ki67 and cyclin B1 were significantly reduced when compared with the model group (P<0.01), while p27^Kip1 expression was significantly increased (P<0.01). The results of the present study suggest that PTX, administered at a non-cytotoxic concentration, may reduce PAH in rats, and prevent the effects of PVR in PAH. These effects of PTX may be associated with increased expression of p27^Kip1 and decreased expression of cyclin B1.

Perivascular medical devices and drug delivery systems: Making the right choices

Perivascular medical devices and perivascular drug delivery systems are conceived for local application around a blood vessel during open vascular surgery. These systems provide mechanical support and/or pharmacological activity for the prevention of intimal hyperplasia following vessel injury. Despite abundant reports in the literature and numerous clinical trials, no efficient perivascular treatment is available. In this review, the existing perivascular medical devices and perivascular drug delivery systems, such as polymeric gels, meshes, sheaths, wraps, matrices, and metal meshes, are jointly evaluated. The key criteria for the design of an ideal perivascular system are identified. Perivascular treatments should have mechanical specifications that ensure system localization, prolonged retention and adequate vascular constriction. From the data gathered, it appears that a drug is necessary to increase the efficacy of these systems. As such, the release kinetics of pharmacological agents should match the development of the pathology. A successful perivascular system must combine these optimized pharmacological and mechanical properties to be efficient.

A Biodegradable Microneedle Cuff for Comparison of Drug Effects through Perivascular Delivery to Balloon-Injured Arteries

Restenosis at a vascular anastomosis site is a major cause of graft failure and is difficult to prevent by conventional treatment. Perivascular drug delivery has advantages as drugs can be diffused to tunica media and subintima while minimizing the direct effect on endothelium. This in vivo study investigated the comparative effectiveness of paclitaxel, sirolimus, and sunitinib using a perivascular biodegradable microneedle cuff. A total of 31 New Zealand white rabbits were used. Rhodamine was used to visualize drug distribution (n = 3). Sirolimus- (n = 7), sunitinib- (n = 7), and paclitaxel-loaded (n = 7) microneedle cuffs were placed at balloon-injured abdominal aortae and compared to drug-free cuffs (n = 7). Basic histological structures were not affected by microneedle devices, and vascular wall thickness of the device-only group was similar to that of normal artery. Quantitative analysis revealed significantly decreased neointima formation in all drug-treated groups (p < 0.001). However, the tunica media layer of the paclitaxel-treated group was significantly thinner than that of other groups and also showed the highest apoptotic ratio (p < 0.001). Proliferating cell nuclear antigen (PCNA)-positive cells were significantly reduced in all drug-treated groups. Sirolimus or sunitinib appeared to be more appropriate for microneedle devices capable of slow drug release because vascular wall thickness was minimally affected.

Unidirectional and sustained delivery of the proresolving lipid mediator resolvin D1 from a biodegradable thin film device

Resolvin D1 (RvD1) belongs to a family of endogenously derived proresolving lipid mediators that have been shown to attenuate inflammation, activate proresolution signaling, and promote homeostasis and recovery from tissue injury. In this study we present a poly(lactic-co-glycolic acid) (PLGA) based thin-film device composed of layers of varying ratios of lactic and glycolic acid that elutes RvD1 unidirectionally to target tissues. The device demonstrated sustained release in vitro for 56 days with an initial burst of release over 14 days. The asymmetric design of the device released 98% of RvD1 through the layer with the lowest molar ratio of lactic acid to glycolic acid, and the remainder through the opposite side. We validated structural integrity of RvD1 released from the device by mass spectrometry and investigated its bioactivity on human vascular endothelial (EC) and smooth muscle cells (VSMC). RvD1 released from the device attenuated VSMC migration, proliferation, and TNF-α induced NF-κB activation, without evidence of cytotoxicity. Delivery of RvD1 to blood vessels was demonstrated ex vivo in a flow chamber system using perfused rabbit aortas and in vivo in a rat carotid artery model, with the devices applied as an adventitial wrap. Our results demonstrate a novel approach for sustained, local delivery of Resolvin D1 to vascular tissue at therapeutically relevant levels. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 31-41, 2017.

Perivascular delivery of resolvin D1 inhibits neointimal hyperplasia in a rat model of arterial injury

OBJECTIVE

Lipid mediators derived from omega-3 polyunsaturated fatty acids such as resolvin D1 (RvD1) accelerate the resolution of inflammation and have potential as vascular therapeutics. The objective of this study was to evaluate local perivascular delivery of RvD1 as a means to attenuate neointimal hyperplasia in a rat model of arterial injury.

METHODS

Smooth muscle cells were harvested from rat aortas to study the effects of RvD1 on rat arterial vascular smooth muscle cell responses in vitro, with focus on inflammation, proliferation, migration, cytoskeletal changes, and cytotoxicity. The safety and efficacy of perivascular delivery of RvD1 through thin biodegradable three-layered poly(lactic-co-glycolic acid) wraps or 25% Pluronic F127 gels were studied in a rat model of carotid angioplasty. A total of 200 ng of RvD1 was loaded into each construct for perivascular delivery after injury. Morphometric and histologic analyses were performed 3 and 14 days after injury.

RESULTS

RvD1 attenuated rat arterial vascular smooth muscle cell inflammatory pathways, proliferation, migration, and mitogen-induced cytoskeletal changes in vitro, without evidence of cytotoxicity. RvD1-loaded wraps reduced neointimal formation after carotid angioplasty by 59% vs no-wrap controls (P = .001) and by 45% vs vehicle-wrap controls (P = .002). RvD1-loaded Pluronic gels similarly reduced neointimal formation by 49% vs no-gel controls (P = .02) and by 52% vs vehicle-gel controls (P = .02). No group was associated with infection, thrombosis, or negative vessel remodeling. Wraps were found to be easier to apply than gel constructs. Ki67 proliferation index was significantly lower in RvD1-loaded wrap-treated arteries compared with both no-wrap and vehicle-wrap controls at both 3 and 14 days after injury (65% vs no-wrap group and 70% vs vehicle-wrap group at day 3, 49% vs both control groups at day 14; P < .05). Similarly, oxidative stress (30% and 29%; P < .05) and nuclear factor κB activation (42% and 45%; P < .05) were significantly lower in the RvD1-loaded wrap group compared with both no-wrap and vehicle-wrap controls at 3 days after injury.

CONCLUSIONS

Local perivascular delivery of RvD1 attenuates formation of neointimal hyperplasia without associated toxicity in a rat model of carotid angioplasty. This effect is likely due to attenuation of inflammatory pathways as well as decreased arterial smooth muscle cell proliferation and migration.

Perivascular biodegradable microneedle cuff for reduction of neointima formation after vascular injury

Restenosis often occurs at the site of vascular grafting and may become fatal for patients. Restenosis at anastomosis sites is due to neointimal hyperplasia (NH) and difficult to treat with conventional treatments. Such abnormal growth of smooth muscle cells in tunica media of vascular tissue can be reduced by delivering anti-proliferation drugs such as paclitaxel (PTX) to the inner vascular layer. Drug eluting stents (DES) or drug eluting balloon (DEB) have been developed to treat such vascular diseases. However, they are less efficient in drug delivery due to the drug loss to blood stream and inadequate to be applied to re-stenotic area in the presence of stent or anastomosis sites. Recently, we have introduced microneedle cuff (MNC) as perivascular delivery devices to achieve high delivery efficiency to tunica media. In this study, we investigated in vivo microneedle insertion and efficacy in treating NH using a rabbit balloon injury model. Microneedle shape was optimized for reliable insertion into tunica media layer. Uniform distribution of PTX in tunica media delivered by MNC devices was also confirmed. Animal study demonstrated significant NH reduction by MNC treatments and much higher delivery efficiency than flat type devices.

Inhibition of intimal hyperplasia by local perivascular application of rapamycin and imatinib mesilate after carotid balloon injury

Purpose

Inhibition of the intimal hyperplasia after vascular surgery is an important issue. The purpose of this study is to define whether perivascular application of rapamycin, imatinib mesylate or cysteamine can reduce intimal hyperplasia in a carotid balloon injury model.

Methods

Each drug was mixed with 40% pluronic gel solution and was topically applied over the injured carotid artery evenly. Two or four weeks after injury, the arteries were harvested and morphometric analysis was done.

Results

The medial areas were not significantly different in each group and a thinning of the media as a toxic drug effect was not observed in any treatment group. The intimal area and intima-to-media (I/M) ratio were significantly reduced in rapamycin-treated group and imatinib-treated group (P < 0.05). But cysteamine-treated group showed a trend of decrease in I/M ratio in 2 weeks, but no difference in 4 weeks.

Conclusion

Perivascular delivery of imatinib or rapamycin with pluronic gel attenuated the development of intimal hyperplasia. But cysteamine did not. Further studies are needed to refine the optimal drug dosages in large animal models.

Perivascular delivery of neomycin inhibits the activation of NF-κB and MAPK pathways, and prevents neointimal hyperplasia and stenosis after arterial injury

The nuclear transcription factor kappaB (NF-kappaB) is a cytoplasmic dimer that, as the family of mitogen-activated protein kinase (MAPK), can directly regulate the expression of early genes and genes involved in the stress response, following a variety of physiological or pathological stimuli. Both of them stimulate the transcription of many proteins, which are considered important during inflammation. A crucial role has been assigned to these factors in cellular proliferation and in neointimal hyperplasia secondary to the endothelial lesion of arterial vessels. On the other hand, it has been described that neomycin can have an inhibitory function on tumor cell proliferation, through the inhibition of different intracellular pathways of signaling, among them the NF-kappaB and MAPK pathways. Rat common carotid artery was subjected to balloon angioplasty. Neomycin sulfate (18 mg) was applied using pluronic acid gel on the adventitial surface of the injured vessel. MAPK and NF-kappaB activation was quantified after 24 hours with immunohistochemical staining. Neointimal formation was quantified after 14 days with morphometry. Immunohistochemistry results demonstrating MAPK and NF-kappaB activation reveal that both transcription factors are activated in the media of the control vessel wall. In contrast, the immunoreactivity for MAPK and NF-kappaB in the sections obtained from arteries treated with neomycin over 24 hours was insufficient or nonexistent. Treatment with neomycin on adventitia over 14 days in arteries on which angioplasty was performed shows a neointimal index (intimal area/medial area) decrease of 71% in comparison with arteries that were not treated. The adventitial neomycin treatment over 14 days produces a very significant increase (287.5%; p<0.0001) in the arterial luminal circumference in comparison with arteries treated with vehicle. These results support the theory that neomycin plays an important role against neointimal hyperplasia through the inhibition of MAPK and NF-kappaB activation.

The effect of short-term intra-arterial delivery of paclitaxel on neointimal hyperplasia and the local thrombotic environment after angioplasty

PURPOSE

To evaluate the effects of short-term intra-arterial delivery of paclitaxel on neointimal hyperplasia and the local thrombotic environment after angioplasty.

METHODS

An experimental common carotid artery injury model was established in 60 rats, which were divided into experimental groups (40 rats) and controls (20 rats). Local intra-arterial administration of paclitaxel was applied at 2 doses (90 and 180 μg/30 μl), and the effects of short-term delivery of paclitaxel on neointimal hyperplasia and the expression of tissue factor (TF), plasminogen activator inhibitor-1 (PAI-1) and tissue-type plasminogen activator (t-PA) were evaluated at days 15 and 30 by hematoxylin and eosin staining and immunohistochemistry.

RESULTS

At 15 and 30 days after injury, neointimal thickness and area, the ratio of intimal area to medial area and the stenotic rate were all significantly decreased in the group provided the high concentrations (180 μg/30 μl) of paclitaxel for 2 min or 10 min and in the group provided the low concentration (90 μg/30 μl) of paclitaxel for 10 min (p < 0.05). At 30 days after injury, there were no significant changes in TF expression among all experimental groups. PAI-1 expression increased in the neointima of the high concentration 10 min group (p < 0.05), while t-PA expression decreased in the neointima of the high concentration 2 min group (p < 0.05).

CONCLUSION

In the rat common carotid artery injury model, the short-term delivery of paclitaxel could effectively inhibit neointimal hyperplasia in the long term, with very little influence on the local expression of TF and PAI-1.

A biodegradable perivascular wrap for controlled, local and directed drug delivery

Perivascular delivery of anti-proliferative agents is an attractive approach to inhibit hyperplasia that causes stenosis of synthetic hemodialysis grafts and other vascular grafts. Perivascular drug delivery systems typically release drugs to both the vascular wall and non-target extravascular tissue. The objective of this study was to develop a biodegradable, perivascular delivery system for localized, sustained and unidirectional drug release in the context of synthetic arteriovenous (AV) grafts used for chronic hemodialysis. To this end, a dense non-porous polymer barrier layer was laminated to either i) a drug-loaded non-porous polymer layer or ii) a porous polymer layer. To provide tunability, the porous layer could be loaded with drug during casting or later infused with a drug-loaded hydrogel. The polymer bilayer wraps were prepared by a solvent casting, thermal-phase inversion technique using either polylactide-co-glycolide (PLGA) or polycaprolactone (PCL). Sunitinib, a multi-target receptor tyrosine kinase inhibitor, was used as a model drug. In a modified transwell chamber system, the barrier function of the non-porous PLGA backing was superior to the non-porous PCL backing although both markedly inhibited drug diffusion. As assessed by in vitro release assays, drug release duration from the drug-loaded non-porous PCL construct was almost 4-fold greater than release from the porous PCL construct infused with drug-laden hydrogel (22 days vs. 5 days); release duration from the drug-loaded non-porous PLGA construct was prolonged approximately 3-fold over release from the porous PLGA construct infused with drug-laden hydrogel (9 days vs. 3 days). Complete in vitro degradation of the PLGA porous and non-porous constructs occurred by approximately 35 days whereas the PCL constructs remained intact even after most of the drug was released (49 days). The PLGA non-porous bilayer wrap containing 143±5.5mg sunitinib in the inner layer was chosen for further pharmacokinetic assessment in vivo where the construct was placed around the external jugular vein in a porcine model. At 1 week, no drug was detected by HPLC/MS/MS in any examined extravascular tissue whereas high levels of drug were detected in the wrapped vein segment (1048 ng g⁻¹ tissue). At 4 weeks, drug was detected in adjacent muscle (52 ng g⁻¹ tissue) but 13-fold greater amounts were detected in the wrapped vein segment (1742 ng g⁻¹ tissue). These results indicate that the barrier layer effectively impedes extravascular drug loss. Tensile testing showed that the initially flexible PLGA construct stiffened with hydration, a phenomenon also observed after in vivo placement. This characteristic may be useful to resist undue circumferential venous tensile stress produced in AV grafting. The PLGA wrap bilayer formulation is a promising perivascular drug delivery design for local treatment of hemodialysis AV graft hyperplasia and possibly other hyperplastic vascular disorders.

Perivascular delivery of blebbistatin reduces neointimal hyperplasia after carotid injury in the mouse

Proliferation and migration of smooth muscle cells (SMC) require myosin II activity; thus, we examined whether blebbistatin, a cell-permeable selective inhibitor of myosin II ATP activity, would impair neointimal hyperplasia after vascular injury. Delivery of blebbistatin via a perivascular polymer cuff reduced neointimal formation by 73% and luminal obstruction by 75% after carotid denudation injury in C57BL/6 mice. Blebbistatin treatment was also associated with a reduction in cell density within the neointima; total number of cells (76 ± 7 to 27 ± 3 cells/high-powered field) and actin-positive cells (64 ± 4 to 24 ± 2 cells/high-powered field) in the neointima were reduced in blebbistatin-treated mice compared with vehicle-treated mice. In a model of vascular injury with an intact endothelium, implantation of a blebbistatin-secreting cuff after carotid ligation in FVB/N mice was associated with a 61% decrease in neointimal area and a significant decrease in luminal obstruction (88 ± 4% in vehicle-treated mice versus 36 ± 4% in blebbistatin-treated mice; p < 0.0001). In cultured rat aortic SMC, blebbistatin disrupted cellular morphology and actin cytoskeleton structure, and these effects were rapid and completely reversible. Blebbistatin had a dose-dependent inhibitory effect on DNA replication and cell proliferative responses to platelet-derived growth factor-BB, angiotensin II, and α-thrombin, migratory responses to serum, and migratory responses after blunt injury. In summary, perivascular delivery of blebbistatin reduced neointimal hyperplasia after carotid injury in the mouse.

Local Cre-mediated gene recombination in vascular smooth muscle cells in mice

Here we describe a means to conditionally modify genes at a predefined and localized region of the vasculature using a perivascular drug delivery device (PDD). A 4-hydroxytamoxifen (4-OHT)-eluting PDD was applied around the carotid or femoral artery of a mouse strain carrying both the tamoxifen-inducible and smooth muscle cell (SMC)-specific Cre-recombinase (SM-Cre-ER(T2)) transgene and a stop-floxed beta-galactosidase gene in the Rosa26 locus: the SM-CreER(T2)(ki)/rosa26 mouse. A dose and time curve of 0-10% (w/w) 4-OHT and 0-14 days application of the PDD in SM-CreER(T2)(ki)/rosa26 mice showed optimal gene recombination at 1% (w/w) 4-OHT loading at 7 days post application (carotid artery 2.4+/-1.8%; femoral artery 4.0+/-3.8% of SMCs). The unique 4-OHT-eluting PDD allowed us to achieve SMC-specific recombination in the same order of magnitude as compared to systemic tamoxifen administration. In addition, recombination was completely confined to the PDD-treated vessel wall segment. Thus, local application of a 4-OHT-eluting PDD results in vascular SMC-specific Cre-mediated recombination in SM-CreER(T2)(ki)/rosa26 mice without affecting additional SMCs.

The safety and efficacy of a paclitaxel-eluting wrap for preventing peripheral bypass graft stenosis: a 2-year controlled randomized prospective clinical study

OBJECTIVES

To compare the safety and efficacy of a bioresorbable paclitaxel-eluting wrap implanted with a synthetic vascular graft (treatment) versus the graft implanted alone (control).

DESIGN

Prospective, randomized, controlled, multicentre, 2-year clinical study conducted in adults scheduled to undergo femoropopliteal peripheral bypass surgery with a polytetrafluoroethylene (PTFE) graft.

MATERIALS AND METHODS

Hundred and nine subjects were randomized 2:1 to treatment or control. All subjects were implanted with a 6mm expanded PTFE vascular graft; in addition, treated subjects had a 2.5 cm x 4 cm paclitaxel-eluting wrap (1.6 microg/mm(2)) placed around the distal graft anastomosis.

RESULTS

The overall incidence of adverse events was similar in both groups. Treated subjects required fewer limb amputations than controls (15.5% vs 18.4%) and time to amputation for those that required amputation was twice as long (153 days vs 76 days). Among diabetics, this effect was pronounced with 13.8% of treated subjects requiring limb amputations compared with 23.5% of controls. Over the course of study, the diameter at the distal graft anastomosis was greater in treated subjects than in controls (difference of 2.1mm at 2 yr, p=0.03).

CONCLUSIONS

The paclitaxel-eluting wrap maintained graft patency at the distal anastomosis and was safe to use in patients who had received a peripheral bypass PTFE graft.

The characterization of paclitaxel-loaded microspheres manufactured from blends of poly(lactic-co-glycolic acid) (PLGA) and low molecular weight diblock copolymers

Paclitaxel-loaded biodegradable drug delivery systems manufactured from poly(lactic-co-glycolic acid) (PLGA) are known to release the drug at extremely slow rates. The objective of this study was to characterize paclitaxel-loaded microspheres composed of blends of PLGA with low molecular weight ampipathic diblock copolymers. The encapsulation and release of a series of poly(epsilon-caprolactone) (PCL)- or poly(D,L-lactic acid) (PDLLA)-co-methoxypolyethylene glycol (MePEG) diblock copolymers was measured using quantitative gel permeation chromatography. Polymeric miscibility was determined by glass transition temperature measurements using differential scanning calorimetry and paclitaxel release was measured using HPLC methods. The PCL- and PDLLA-based diblock copolymers encapsulated at high efficiency and were miscible in PLGA microspheres (30-120m microm size range). The burst phase of paclitaxel release was increased up to 20-fold by the inclusion of diblock copolymers in PLGA microspheres. Approximately 10% of the more hydrophobic PCL-based copolymers released from the microspheres in a short burst over 3 days followed by very slow release over the following 10 weeks. Only the PDLLA-based copolymer released from the PLGA microspheres in a controlled manner over 10 weeks. All microspheres containing PEG were found to have more hydrophilic surfaces (as measured by contact angle) with improved biocompatibility (reduced neutrophil activation) compared to PLGA only microspheres. These results indicate that low molecular weight polyester-based diblock copolymers may be effectively encapsulated in PLGA microspheres to increase paclitaxel release (probably through a micellization process) and improve biocompatibility.

Epothilone D, a microtubule-stabilizing compound, inhibits neointimal hyperplasia after rat carotid artery injury by cell cycle arrest via regulation of G1-checkpoint proteins

Epothilone D (Epo-D) is a paclitaxel-like microtubule-stabilizing agent that was isolated from the myxobacterium Sorangium cellulosum. Although Epo-D can inhibit proliferation in multiple tumor cell lines, the effect of Epo-D on neointimal hyperplasia after angioplasty has not been reported. The aim of the present study was to investigate the effects of Epo-D on neointimal hyperplasia using an in vivo rat carotid artery injury model. We demonstrated that local Epo-D treatment significantly reduced neointimal hyperplasia after in vivo rat carotid artery injury, and Epo-D potently inhibited DNA synthesis, cell cycle progression and cell proliferation after FBS- and PDGF-BB-stimulation; PDGF-BB has been identified as the most potent growth factor for stimulating the proliferation of activated rat aortic smooth muscle cells (RASMCs). To clarify the specific effects of Epo-D on cell cycle machinery, we examined its effects on cyclin-dependent kinase (CDK)2, CDK4, cyclin E, p27, and retinoblastoma (Rb) proteins as cell cycle-related proteins in cellular lysates from PDGF-BB-stimulated RASMCs. Epo-D treatment significantly decreased the level of CDK2 protein, but did not change the levels of CDK4 and cyclin E proteins. Furthermore, Epo-D inhibited the phosphorylation of Rb, a key regulator of the G1 to S phase transition in the cell cycle. These findings suggest that Epo-D may regulate the cell cycle G1-checkpoint proteins as its major molecular mechanism for inhibiting neointimal hyperplasia after in vivo rat carotid artery injury.

Epothilone B Inhibits Neointimal Formation after Rat Carotid Injury through the Regulation of Cell Cycle-Related Proteins

The abnormal proliferation of vascular smooth muscle cells (VSMCs) in arterial walls is an important pathogenetic factor of vascular disorders such as atherosclerosis and restenosis after angioplasty. Epothilone B, a novel potential antitumor compound, has a potent effect on preventing postangioplasty restenosis. Therefore, we established an in vivo rat carotid injury model and examined the potential effects of epothilone B on cardiovascular disease. We found that epothilone B potently prevented neointimal formation and in vivo VSMCs proliferation. In addition, we also showed that epothilone B significantly inhibited 5% fetal bovine serum (FBS)- and 50 ng/ml platelet-derived growth factor (PDGF)-BB-induced proliferation and cell cycle progression in rat aortic VSMCs. Furthermore, FBS and PDGF-BB induced the activations of extracellular signal-regulated kinases 1 and 2, Akt, phospholipase C gamma 1, and PDGF-receptor beta chain tyrosine kinase were not changed by epothilone B. However, epothilone B treatment caused a significant decrease in the level of cyclin-dependent protein kinase (CDK) 2, whereas it caused no change in the levels of cyclin E and down-regulated the phosphorylation of retinoblastoma, which plays a critical role in cell cycle regulation. Furthermore, levels of p27, an inhibitor of cyclin E/CDK2 complex, were significantly increased in VSMCs treated with epothilone B, indicating that this might be a major molecular mechanism for the inhibitory effects of epothilone B on the proliferation and cell cycle of VSMCs. These findings suggest that epothilone B can inhibit neointimal formation via the cell cycle arrest by the regulation of the cell cycle-related proteins in VSMCs.

The Taxus drug-eluting stent: a new paradigm in controlled drug delivery

The advent of drug-eluting stents (DES) has provided the medical community with a technology that is transforming the treatment of coronary artery disease. As the newest treatment modality available to the interventional cardiologist, drug-eluting stents have not only significantly reduced the risk of restenosis, but they are also allowing the interventionalists to treat more complex lesions in patients that would otherwise require more invasive bypass surgery. Development of these drug-device combination products has presented considerable challenges to the device industry because it involves a multi-disciplinary approach that combines conventional device design and manufacturing with the principles of controlled local drug delivery. This review article provides an in-depth discussion of the key elements of drug-eluting stents, focusing on the TAXUS paclitaxel-eluting stent as an example of this new class of product. Specific sections will review the drug and polymer matrix components, formulation development and evaluation, pre-clinical studies and clinical trial results.

Drug-eluting stents: a multidisciplinary success story

Coronary stenting is the most common form of interventional treatment for symptomatic coronary artery disease. In-stent restenosis following bare metal stent (BMS) placement is the most common cause of procedural failure and occurs as a result of vessel wall trauma secondary to balloon angioplasty and stent deployment that results in an overly aggressive healing response (neointimal hyperplasia) that overgrows the stent lumen and causes vascular narrowing. Drug-eluting stents (DES) are specialized vascular stents capable of delivering drugs to the arterial wall in a controlled manner such that neointimal hyperplasia is reduced or prevented, luminal patency is preserved, coronary blood flow is maintained and the patient is spared a repeat procedure to re-open the vessel. The objectives of the review are to provide an overview of the major contributions that a broad range of disciplines have made to the design and development of drug-eluting stents and to summarize future directions of these fields of research. Engineers and biomaterials scientists have explored relationships between stent design and stent performance and work continues to optimize stent design and biocompatibility of stent biomaterials. Pharmaceutical scientists are continually expanding the range of candidate drugs for pharmacological intervention, and improving the technology using novel coatings to modulate drug release. Clinical scientists are investigating issues such as long-term safety and efficacy, new applications of drug-eluting stents and optimal deployment techniques.

Locally administered antiproliferative drugs inhibit hypercontractility to serotonin in balloon-injured pig coronary artery

Although drugs such as sirolimus and paclitaxel are effective in reducing restenosis, their effects on vascular function are often overlooked. In this study, we have examined the effects of local delivery of several anti-restenotic drugs given in vivo after balloon injury on in vitro vascular contraction and relaxation 28 days after injury. Paclitaxel (50 microM), the farnesyl protein transferase inhibitor L744 (25 microM), sirolimus (25 microM) and Van 10/4 (decahydro-1,1,4,7-tetramethyl-1H-cycloprop[e]azulen-4-o-[2-(3-methylpent-2-enoyl)-fucopyranoside]; 25 microM) were delivered to porcine coronary arteries in vivo and the arteries removed 28 days later. Contractions to KCl and 5-hydroxytryptamine (5-HT) and relaxations to calcimycin and 3-morpholinosydnonimine (SIN-1) were measured in control (LCx) and balloon-injured (LAD) rings. In vehicle-infused coronary arteries, contraction to KCl and 5-HT was significantly enhanced 28 days after balloon injury, while the response to calcimycin had recovered fully, indicating endothelial regrowth. The response to SIN-1 was unchanged. None of the four drugs tested had any effect on the enhanced response to KCl 28 days after injury or on recovery of the calcimycin response. The hyper-responsiveness to 5-HT was eliminated by sirolimus, Van 10/4 and L744, but not paclitaxel. This study demonstrates that local drug infusion with structurally different antiproliferative drugs at the time of balloon angioplasty does not affect endothelial recovery and may in some cases prevent hyper-responsiveness to constrictor agents.

The drug-based pipeline against restenosis

More than 1 million percutaneous coronary interventions (PCIs) are performed yearly worldwide. Restenosis is the recurrent narrowing that can occur within 6 months following an initially successful PCI. Although drug-eluting stents have accomplished remarkable success, restenosis has not been eliminated and optimisation of both the polymers and drugs associated with them is desirable. This article reviews the presently available and potential preventive approaches against restenosis, including the sirolimus and paclitaxel drug-eluting stents.

Characterization of perivascular poly(lactic-co-glycolic acid) films containing paclitaxel

The objectives of this study were to investigate the use of poly(lactic-co-glycolic acid) (PLGA) for the formulation of paclitaxel loaded films and to characterize these films for potential application as perivascular "wraps" to prevent restenosis. Films were manufactured from PLGA blended with either methoxypolyethylene glycol (MePEG) or a diblock copolymer composed of poly(D,L-lactic acid)-block-methoxypolyethylene glycol, PDLLA-MePEG (diblock) by solvent evaporation on teflon discs. Elasticity was determined by gravimetric stress/strain analysis. Thermal analysis was determined using differential scanning calorimetry (DSC). Changes in film composition and degradation in aqueous media were determined using gel permeation chromatography (GPC). Paclitaxel release from films was measured by incubation of the films in phosphate buffered saline (PBS) with drug analysis by HPLC methods. The addition of MePEG or diblock to PLGA caused a concentration dependent increase in the elasticity of films, due to plasticizing effects. DSC analysis showed that MePEG and diblock caused a concentration dependent decrease in the glass transition temperature (Tg) of PLGA indicating miscibility of the polymers. When placed in aqueous media, more than 75% of MePEG dissolved out of the PLGA films within 2 days, whereas diblock partitioned slowly and in a controlled manner out of the films. Paclitaxel release from PLGA/MePEG films was very slow with less than 5% of the encapsulated drug being released over 2 weeks. The addition of 30% diblock to paclitaxel loaded PLGA films caused a substantial increase (five- to eight-fold) in the release rate of paclitaxel. PLGA films containing 30% diblock and either 1% or 5% paclitaxel were partially or completely degraded following perivascular implantation in rats.

The Effects of Paclitaxel on the Three Phases of Restenosis

PURPOSE

We sought to evaluate the growth-modulating potential of paclitaxel on cultured human arterial smooth muscle cells depending on the administered dose.

MATERIAL AND METHODS

For all experiments human arterial smooth muscle cells (SMCs) were used. SMCs were either cultured for 5 days or for 20 days with paclitaxel (doses: 10(-7) M, 10(-8) M, 10(-9) M). For a total period of 20 days, proliferation kinetics of the SMC were analyzed. To assess the clonogenic activity of the SMC colony-forming assays were performed. Drug- and dose-dependent cell cycle changes were analyzed by flow cytometry. The effect on cell migration was examined in a 2-chamber migration system. The effects of paclitaxel on the synthesis of tenascin were examined via immunofluorescence.

RESULTS

Depending on the dose administered, paclitaxel proved to inhibit SMC proliferation effectively when administered during the total period of 20 days. When incubated for 5 days with doses of paclitaxel ranging between 10(-8) M and 10(-9) M, SMCs showed clear signs of regeneration. When being incubated with 10(-7) M of paclitaxel, however, SMCs reacted with a reduction in cell proliferation, a reduced clonogenic activity, and a drug-induced G2/M phase block. SMC migration was inhibited effectively as well as extracellular matrix formation.

CONCLUSION

Paclitaxel is a potent inhibitor of SMC proliferation, SMC migration, and extracellular matrix formation in vitro, with all three phases of the restenosis process inhibited effectively.

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.

A polymer-based, paclitaxel-eluting stent in patients with coronary artery disease

BACKGROUND

Restenosis after coronary stenting necessitates repeated percutaneous or surgical revascularization procedures. The delivery of paclitaxel to the site of vascular injury may reduce the incidence of neointimal hyperplasia and restenosis.

METHODS

At 73 U.S. centers, we enrolled 1314 patients who were receiving a stent in a single, previously untreated coronary-artery stenosis (vessel diameter, 2.5 to 3.75 mm; lesion length, 10 to 28 mm) in a prospective, randomized, double-blind study. A total of 652 patients were randomly assigned to receive a bare-metal stent, and 662 to receive an identical-appearing, slow-release, polymer-based, paclitaxel-eluting stent. Angiographic follow-up was prespecified at nine months in 732 patients.

RESULTS

In terms of base-line characteristics, the two groups were well matched. Diabetes mellitus was present in 24.2 percent of patients; the mean reference-vessel diameter was 2.75 mm, and the mean lesion length was 13.4 mm. A mean of 1.08 stents (length, 21.8 mm) were implanted per patient. The rate of ischemia-driven target-vessel revascularization at nine months was reduced from 12.0 percent with the implantation of a bare-metal stent to 4.7 percent with the implantation of a paclitaxel-eluting stent (relative risk, 0.39; 95 percent confidence interval, 0.26 to 0.59; P<0.001). Target-lesion revascularization was required in 3.0 percent of the group that received a paclitaxel-eluting stent, as compared with 11.3 percent of the group that received a bare-metal stent (relative risk, 0.27; 95 percent confidence interval, 0.16 to 0.43; P<0.001). The rate of angiographic restenosis was reduced from 26.6 percent to 7.9 percent with the paclitaxel-eluting stent (relative risk, 0.30; 95 percent confidence interval, 0.19 to 0.46; P<0.001). The nine-month composite rates of death from cardiac causes or myocardial infarction (4.7 percent and 4.3 percent, respectively) and stent thrombosis (0.6 percent and 0.8 percent, respectively) were similar in the group that received a paclitaxel-eluting stent and the group that received a bare-metal stent.

CONCLUSIONS

As compared with bare-metal stents, the slow-release, polymer-based, paclitaxel-eluting stent is safe and markedly reduces the rates of clinical and angiographic restenosis at nine months.

Paclitaxel-Eluting Stents: Are They All Equal? An Analysis of Six Randomized Controlled Trials in De Novo Lesions of 3,319 Patients

In Germany, four different drug eluting stents (DES) systems are currently commercially available. Whereas sirolimus has been clinically tested in only a single type of stent with a single type of coating in only a single dose, paclitaxel has been tested on various stent designs, in various dose densities, and in various release formulations with or without a polymer carrier. Therefore, the question arises: are all paclitaxel stents equally safe and effective? Six clinical randomized trials investigated the safety and efficacy of paclitaxel-eluting stents in patients with de-novo lesions: TAXUS-I (61 pats), TAXUS-II (536 pats), ASPECT (177 pats), ELUTES (190 pats), DELIVER-I (1041 pats) and TAXUS-IV (1314 pats). In the TAXUS-series, paclitaxel released from the stent was controlled by the Translute polymer. In the other studies, however, no polymer carrier was used. In TAXUS-I, II & IV, the dose density of 1 microg/mm2 significantly reduced angiographic parameters of restenosis and improved clinical outcomes. In ASPECT and ELUTES there was a dose-dependent effect on angiographic parameters of restenosis with the best results for a paclitaxel dose density of approximately 3.0 microg/mm2. Clinical outcomes at 6 and 12 months, however, were not improved in these studies without coating. The studies unanimously show that the paclitaxel-eluting stents are safe, if clopidogrel is added to ASA for 3 to 6 months. The safety of paclitaxel-eluting stents is independent of the stent design, the dose density and the presence or absence of a polymer carrier system. For paclitaxel-eluting stents using a polymer carrier, the dose density of 1 microg/mm2 is highly effective, whereas for paclitaxel-eluting stents without a polymer carrier, the minimal effective dose density is much higher (3 microg/mm2). Despite their improvement of angiographic parameters, paclitaxel-eluting stents without a polymer carrier did not demonstrate a positive effect on clinical outcome. In contrast, polymer-based paclitaxel elution produced significant clinical benefit.

Inhibitor of apoptosis protein survivin regulates vascular injury

Survivin (also termed Birc5) belongs to the family of genes known as inhibitors of apoptosis, and it has been implicated in both prevention of cell death and control of mitosis. The survivin pathway is exploited in cancer, but its potential role in vascular injury is unknown. Here, we show that balloon-mediated arterial injury in rabbits resulted in expression of survivin in vascular cells. Serum or PDGF-AB stimulated survivin expression in cultured smooth-muscle cells (SMCs), which suppressed apoptosis and prevented caspase activation. Adenoviral delivery of a phosphorylation-defective survivin mutant reversed the cytoprotective effect of PDGF in SMCs without affecting mitotic progression, suppressed neointimal formation in wire-injured mouse femoral arteries, and induced vascular cell apoptosis in vivo. These data identify survivin as a critical regulator of SMC apoptosis after acute vascular injury. Disrupting the survivin pathway may provide a novel therapy to limit pathological vessel-wall remodeling.