Therapeutic Potential of Oral Antiproliferative Agents in the Prevention of Coronary Restenosis

Therapeutic potential for protein kinase C inhibitor in vascular restenosis

Vascular restenosis, an overreaction of biological response to injury, is initialized by thrombosis and inflammation. This response is characterized by increased smooth muscle cell migration and proliferation. Available pharmacological treatments include anticoagulants, antiplatelet agents, immunosuppressants, and antiproliferation agents. Protein kinase C (PKC), a large family of serine/threonine kinases, has been shown to participate in various pathological stages of restenosis. Consequently, PKC inhibitors are expected to exert a wide range of pharmacological activities therapeutically beneficial for restenosis. In this review, the roles of PKC isozymes in platelets, leukocytes, endothelial cells, and smooth muscle cells are discussed, with emphasis given to smooth muscle cells. We will describe cellular and animal studies assessing prevention of restenosis with PKC inhibitors, particularly targeting -α, -β, -δ, and -ζ isozymes. The delivery strategy, efficacy, and safety of such PKC regulators will also be discussed.

Neointimal hyperplasia and vasoreactivity are controlled by genetic elements on rat chromosome 3

Neointimal hyperplasia (NIH) can lead to restenosis after clinical vascular interventions. NIH results from complex and poorly understood interactions between signaling cascades in the extracellular matrix and the disrupted endothelium, which lead to vessel occlusion. Quantitative trait loci (QTLs) were reported previously on rat chromosomes 3 and 6 through linkage analysis of postinjury NIH in midiliac arterial sections. In the current study, substitution mapping validated the RNO3 NIH QTL but not the RNO6 NIH QTL. The SHR.BN3 congenic strain had a 3-fold increase in the percentage of NIH compared with the parental spontaneously hypertensive rat strain. A double congenic study of RNO3+RNO6 NIH QTL segments suggested less than additive effects of these 2 genomic regions. To test the hypothesis that changes in vessel dynamics account for the differences in NIH formation, we performed vascular reactivity studies in the Brown Norway (BN), spontaneously hypertensive rat (SHR), SHR.BN3, and SHR.BN6 strains. De-endothelialized left common carotid artery rings of the SHR.BN3 showed an increased vascular responsiveness when treated with serotonin or prostaglandin F2(alpha), with significant differences in EC(50) and maximum effect (P<0.01) values compared with the spontaneously hypertensive rat parental strain. Because both vascular reactivity and percentage of NIH formation in the SHR.BN3 strain are significantly higher than the SHR strain, we postulate that these traits may be associated and are controlled by genetic elements on RNO3. In summary, these results confirm that the RNO3 NIH QTL carries the gene(s) contributing to postinjury NIH formation.

Avoiding restenosis: is there a role for glucocorticoids in the drug-eluting stent era?

Restenosis is an important limitation of percutaneous coronary interventions (PCI). In-stent restenosis is mainly due to neointimal hyperplasia, a proliferative process modulated by inflammatory mechanisms. Numerous technical and pharmacological means have been tested to reduce restenosis rates, with frequently disappointing clinical results. Drug-eluting stents (DES) have demonstrated a high efficacy in reducing restenosis, but there are some associated problems that limit its generalized utilization. Glucocorticoids (GC), as potent anti-inflammatory agents, may exert beneficial effects on neointimal proliferation. Clinical studies with oral and intracoronary GC therapy have demonstrated reduction in restenosis rates in selected patients. Although further investigations are warranted, GC might have a potential role for restenosis prevention in selected cases.

Predicting in vivo efficacy of potential restenosis therapies by cell culture studies: species-dependent susceptibility of vascular smooth muscle cells

Although drug-eluting stents (DES) are successfully utilized for restenosis therapy, the development of local and systemic therapeutic means including nanoparticles (NP) continues. Lack of correlation between in vitro and in vivo studies is one of the major drawbacks in developing new drug delivery systems. The present study was designed to examine the applicability of the arterial explant outgrowth model, and of smooth muscle cells (SMC) cultures for prescreening of possible drugs. Elucidation of different species sensitivity (rat, rabbit, porcine and human) to diverse drugs (tyrphostins, heparin and bisphsophonates) and a delivery system (nanoparticles) could provide a valuable screening tool for further in vivo studies. The anticipated sensitivity ranking from the explant outgrowth model and SMC mitotic rates (porcine>rat>>rabbit>human) do not correlate with the observed relative sensitivity of those animals to antiproliferative therapy in restenosis models (rat≥rabbit>porcine>human). Similarly, the inhibitory profile of the various antirestenotic drugs in SMC cultures (rabbit>porcine>rat>>human) do not correlate with animal studies, the rabbit- and porcine-derived SMC being highly sensitive. The validity of in vitro culture studies for the screening of controlled release delivery systems such as nanoparticles is limited. It is suggested that prescreening studies of possible drug candidates for restenosis therapy should include both SMC cell cultures of rat and human, appropriately designed with a suitable serum.

Effect of cilostazol on in-stent neointimal hyperplasia after coronary artery stenting: a quantative coronary angiography and volumetric intravascular ultrasound study

BACKGROUND

This study was designed to investigate the efficacy of cilostazol on the prevention of in-stent neointimal hyperplasia as measured by both quantitative coronary angiography (CAG) and volumetric intravascular ultrasound (IVUS).

METHODS AND RESULTS

Fifty-nine patients (39 men, age 62 years) undergoing elective coronary stenting were randomly assigned to receive aspirin plus clopidogrel or ticlopidine (Group I, n=28, 30 lesions) or aspirin plus clopidogrel or ticlopidine plus cilostazol (Group II, n=31, 35 lesions). CAG and IVUS were performed and repeated at 6 months to assess the primary endpoints of minimal luminal diameter (MLD) and in-stent neointimal hyperplasia volume. Follow-up CAG was performed on all patients and follow-up IVUS study was available for 50 lesions in 48 patients (24 lesions in Group I, 26 in Group II). There were no significant differences in the baseline angiographic data between the 2 groups. At 6 months follow-up, in-stent MLD was 1.90+/-0.76 mm in Group I and 2.41+/-0.85 mm in Group II (p=0.006). Volumetric IVUS at 6 months demonstrated that in-stent intimal hyperplasia volume per stent length was 2.2+/-1.4 mm3/mm in Group I and 1.0+/-0.5 mm3/mm in Group II (p=0.001).

CONCLUSIONS

Triple antiplatelet therapy including cilostazol seems to be more effective at preventing in-stent neointimal hyperplasia than a dual antiplatelet regimen.

Photodynamic Therapy Reduces Intimal Hyperplasia in Prosthetic Vascular Bypass Grafts in a Pig Model

BACKGROUND

Bypass surgery has a failing frequency of 30% during the first year, mainly due to intimal hyperplasia (IH). This negative effect is most pronounced in artificial grafts. Photodynamic therapy (PDT) is a technique in which light activates photosensitizer dyes to produce free-radicals resulting in an eradication of cells in the vascular wall. The aim of this study was to determine the effectiveness of PDT to reduce IH in a preclinical porcine PTFE bypass model.

MATERIAL AND METHODS

Ten pigs were used. After a pilot PDT dosimetry study (n=3) PTFE grafts were bilaterally placed into the circulation as bypasses from the common to the external iliac arteries (n=7). The right sides served as controls (C). Before implantation of the left grafts, the arterial connecting sites of the left distal anastomoses were PDT-treated. The arteries were pressurized at 180 mmHg for 5 minutes with the photosensitizer Methylene Blue (330 microg/ml), and thereafter endoluminally irradiated with laser light (lambda = 660 nm, 100 mW/cm(2), 150 J/cm(2)). After 4 weeks the specimens were retrieved and formalin fixed. Cross sections through the midportions of the distal anastomoses and the grafts were used for histology, immunohistochemistry to identify inflammatory cells and morphometric evaluation (n=7).

RESULTS

No systemic side effects and no graft occlusions were noted. PDT-treated anastomoses showed reduced IH in the mid-portions of the anastomoses (Area of IH: microm(2)/microm graft: C: 6970+/-1536, PDT: 2734+/-2560; P<0.005) as well as in the grafts (C: 5391+/-4031, PDT: 777+/-1331; P<0.02). The number of inflammatory cells per microscopic field was increased after PDT (C: 24+/-16, PDT: 37+/-15; P<0.009).

CONCLUSIONS

Adjuvant PDT, performed in an endovascular fashion, was a safe method to reduce prosthetic graftstenosis in a preclinical setting. This study underscores the clinical potential of PDT to inhibit the development of clinical bypass graftstenosis.

Effect of thiazolidinedione therapy on restenosis after coronary stent implantation: a meta-analysis of randomized controlled trials

BACKGROUND

We sought to review the evidence from the available randomized controlled trials (RCTs) regarding the effect of thiazolidinedione therapy on in-stent restenosis after percutaneous coronary intervention.

METHODS

The studies in our meta-analysis were retrieved from search on the PubMed database and from references in relevant articles. Included studies were RCTs that provided comparative data regarding the effectiveness of 6-month pioglitazone or rosiglitazone therapy on the prevention of in-stent restenosis after coronary stent implantation as assessed by quantitative coronary angiography.

RESULTS

Five RCTs that included 235 evaluable patients who underwent coronary stent implantation and received a 6-month pioglitazone or rosiglitazone therapy were included in our meta-analysis. Restenosis rate was significantly lower in patients who received thiazolidinedione therapy in addition to standard therapy (3 RCTs, 170 patients, odds ratio 0.29, 95% CI 0.15-0.56, random effects model). Percentage diameter stenosis was significantly lower in the pioglitazone-rosiglitazone arm (3 RCTs, 170 patients, weighted difference in means 14.35, 95% CI 19.99-8.72, random effects model). Minimal lumen diameter of the target lesion was significantly higher in patients who received thiazolidinedione therapy (3 RCTs, 170 patients, weighted difference in means 0.43, 95% CI 0.21-0.65, random effects model). Patients who received thiazolidinediones were significantly less likely to undergo target lesion revascularization due to restenosis (4 RCTs, 197 patients, odds ratio 0.24, 95% CI 0.09-0.61, random effects model).

CONCLUSIONS

Our study suggests that thiazolidinedione therapy in patients undergoing coronary stent implantation may be associated with less in-stent restenosis and repeated revascularization. Decisions on clinical use of this therapy must await larger double-blind clinical trials.

Concurrent delivery of dexamethasone and VEGF for localized inflammation control and angiogenesis

Localized elution of corticosteroids has been used in suppressing inflammation and fibrosis associated with implantation and continuous in vivo residence of bio-medical devices. However, these agents also inhibit endogenous growth factors preventing angiogenesis at the local tissue, interface thereby delaying the healing process and negatively impacting device performance. In this work, a combination of dexamethasone and vascular endothelial growth factor (VEGF) was investigated for concurrent localized delivery using PLGA microsphere/PVA hydrogel composites. Pharmacodynamic effects were evaluated by histopathological examination of subcutaneous tissue surrounding implanted composites using a rat model. The hydrogel composites were capable of simultaneously releasing VEGF and dexamethasone with approximately zero order kinetics. Composites were successful in controlling the implant/tissue interface by suppressing inflammation and fibrosis as well as facilitating neo-angiogenesis at a fraction of their typical oral or i.v. bolus doses. Implants containing VEGF showed a significantly higher number of mature blood vessels at the end of the 4 week study irrespective of the presence of dexamethasone. Thus, localized concurrent elution of VEGF and dexamethasone can overcome the anti-angiogenic effects of the corticosteroid and can be used to engineer inflammation-free and well-vascularized tissue in the vicinity of the implant. These PLGA microsphere/PVA hydrogel composites show promise as coatings for implantable bio-medical devices to improve biocompatibility and ensure in vivo performance.

Pilot study with an intensified oral sirolimus regimen for the prevention of in-stent restenosis in de novo lesions: a serial intravascular ultrasound study

This pilot study evaluated the safety and efficacy of an intensified oral sirolimus regimen (15-mg loading dose 24 hr before PCI, followed by a daily dose of 5 mg for 4 weeks) in 15 patients subjected to elective bare metal coronary stent implantation for de novo lesions. Mean patient age was 59+/-9; 73% were male, and 13% were diabetic patients. The reference diameter was 3.04+/-0.38 mm, and the lesion length was 14+/-2 mm. Angiographic and volumetric intravascular ultrasound (IVUS) analyses were performed in all patients at 6.0+/-0.2 months. Two patients (13%) met the definition of in-segment binary restenosis; in-stent and in-segment angiographic late loss was 0.61+/-0.31 mm and 0.67+/-0.45 mm, respectively, and the percent neointimal volume was 28.5+/-15.8%. At adjacent reference segments, there was neither significant plaque increase nor constrictive vascular remodeling. At 24-month follow-up no deaths, myocardial infarctions, or target lesion revascularizations were detected. Mean sirolimus blood level was 13+/-7 ng/ml. No correlations were found between drug levels and late loss (r=0.15, P=0.59) or IVUS percent neointimal volume (r=0.23, P=0.47). Side effects were frequent (80%), leading to dose reductions in four and drug discontinuation in one patient. The results of this pilot study suggest that an intensified 5-mg oral sirolimus regimen resulted in no relevant improvements in the angiographic and IVUS parameters of restenosis after stent implantation in de novo lesions when compared with historic controls. Considering the efficacy/safety balance, our results do not encourage further trials evaluating the current protocol for the prevention of in-stent restenosis.

Linkage analysis of neointimal hyperplasia and vascular wall transformation after balloon angioplasty

Neointimal hyperplasia (NIH), a result of vascular injury, is due to the migration and proliferation of smooth muscle cells through the media and internal elastic lamina leading to vascular occlusion. We used a rat model to find the genetic regions controlling NIH after endothelial denudation in two divergent inbred strains of rats. The Brown Norway (BN) and spontaneously hypertensive rat (SHR) strains have a 2.5-fold difference in injury-induced NIH. A population of 301 F2(SHR × BN) rats underwent a standard vascular injury followed by phenotyping 8 wk after injury to identify quantitative trait loci (QTL) responsible for this strain difference. Interval mapping identified two %NIH QTL on rat chromosomes 3 and 6 [logarithm of odds (LOD) scores 2.5, 2.2] and QTL for other injured vascular wall changes on rat chromosomes 3, 4, and 15 (LOD scores 2.0–4.6). Also, QTL for control vessel media width (MW) and media area (MA) were found on chromosome 6 with LOD scores of 2.3 and 2.5, suggesting that linkage exists between these control vessel parameters and NIH production. These results represent the first genetic analysis for the identification of NIH QTL and QTL associated with the vascular injury response.

Dexamethasone could improve myocardial infarction outcomes and provide new therapeutic options for non-interventional patients

BACKGROUND

Statins reduce death and morbidity of acute myocardial infarction in part through immunosuppressive mechanisms, suggesting glucocorticoids could produce similar benefits. Glucocorticoids inhibit proliferation of smooth muscle cells and activation of macrophages within atherosclerotic plaques and protect ischemic myocardium through inhibition of a heat shock protein. Dexamethasone-eluting coronary stents have a decreased rate of restenosis, and oral prednisone reduces restenosis of conventional stents. Some studies from the 1970's and 1980's showed that steroids improve survival in myocardial infarction, but no conclusive large-scale randomized well-powered trials have been conducted.

PRESENTATION OF THE HYPOTHESIS

Dexamethasone administered alongside statins in the setting of acute myocardial infarction could attenuate myocardial damage in patients with diffuse disease.

TESTING THE HYPOTHESIS

Patients with acute myocardial infarction who cannot undergo angioplasty or coronary artery bypass grafting could be given a statin and intravenous and oral dexamethasone. Dexamethasone minimizes fluid retention and avoids mineralocorticoid-induced cell proliferation in plaques. Blood glucose monitoring should be ordered for all patients, but diabetic patients need not be excluded. There should be measures to prevent steroid-induced homocystinuria or more common complications such as ulcers, osteoporosis, infections and psychosis.

IMPLICATIONS OF THE HYPOTHESIS

Showing that acute coronary syndrome is a steroid-responsive disorder would have immediate relevance for patients limited to medical management because of anatomy and comorbidities, and results would similarly have application for acute ischemic stroke.

Restenosis related to percutaneous coronary intervention has been solved?

Percutaneous coronary intervention (PCI) has become the most important revascularization method in the treatment of coronary artery disease. The major problem in PCI has been renarrowing of the dilated vessel after the procedure (restenosis). The best results in the prevention of restenosis have been obtained by covering the stent with drugs that inhibit cellular growth, thus limiting excessive scar formation inside of the stent. With drug-eluting stents, restenosis has been reduced to one-tenth compared with balloon angioplasty and to one-fourth compared to bare metal stents. Due to drug-eluting stents, PCI is an alternative to bypass surgery. However, restenosis will remain a challenge due to the increased number of procedures and more difficult disease treated with PCI.

2005 Dr. Gary J. Becker Young Investigator Award: Periprocedural Oral Administration of the Leflunomide Analogue FK778 Inhibits Neointima Formation in a Double-injury Rat Model of Restenosis

PURPOSE

To test the efficacy of limited oral administration of the new leflunomide analogue FK778 for suppression of neointima proliferation in a double-injury restenosis model in the rat.

MATERIALS AND METHODS

For induction of aortic lesions, silicon cuffs were placed operatively around the infrarenal aortas of Lewis rats. After 21 days, the aortic cuffs were removed and the lesions were dilated with 2-F Fogarty catheters inserted via the left common carotid artery. The novel immunosuppressant FK778 was administered at a dose of 5 mg/kg body weight (group 1) or 15 mg/kg body weight (group 2) in a total of 38 animals. For both doses, three different periinterventional time periods, each with a 5-day course of oral FK778, were defined as follows: (i) days -2 to 2, (ii) days 1-5, and (iii) days 7-11, with six or seven rats in each group. After 3 weeks, intima/media ratios were assessed morphometrically and immunohistochemistry for quantification of intimal alpha-actin expression was performed.

RESULTS

In both dose groups, there was a trend toward inhibition of neointima formation when the 5-day course of FK778 was started before or 1 day after the intervention. However, in the lower-dose group, inhibition of neointima was not statistically significant regardless of the time frame of treatment (groups 1a-c). With the higher dose, suppression of intimal hyperplasia was significant when FK778 was administered between days 1 and 5 after angioplasty (group 2b; P<.01). Expression of alpha-actin in the intima of FK778-treated rats was significantly reduced when the drug was started 2 days before angioplasty in group 1a (P<.05) or 1 day after angioplasty in both dosage groups (group 1b, P<.01; group 2b, P<.05).

CONCLUSION

In the double-injury rat model presented, balloon-mediated proliferation of smooth muscle cells in the intima with consecutive intimal thickening was influenced by FK778 in a dose-dependent manner. However, long-term studies are needed to exclude a delay of vascular healing in this particular model.