Intracoronary radiotherapy for restenosis

Intratumoural administration of dendritic cells: hostile environment and help by gene therapy

Like paratroopers in special operations, dendritic cells (DCs) can be deployed behind the enemy borders of malignant tissue to ignite an antitumour immune response. 'Cross-priming T cell responses' is the code name for their mission, which consists of taking up antigen from transformed cells or their debris, migrating to lymphoid tissue ferrying the antigenic cargo, and meeting specific T cells. This must be accomplished in such an immunogenic manner that specific T lymphocytes would mount a robust enough response as to fully reject the malignancy. To improve their immunostimulating activity, local gene therapy can be very beneficial, either by transfecting DCs with genes enhancing their performance, or by preparing tumour tissue with pro-inflammatory mediators. In addition, endogenous DCs from the tumour host can be attracted into the malignant tissue following transfection of certain chemokine genes into tumour cells. On their side, tumour stroma and malignant cells set up a hostile immunosuppressive environment for artificially released or attracted DCs. This milieu is usually rich in transforming growth factor-beta, vascular endothelial growth factor, and IL-10, -6 and -8, among other substances that diminish DC performance. Several molecular strategies are being devised to interfere with the immunosuppressive actions of these substances and to further enhance the level of anticancer immunity achieved after artificial release of DCs intratumourally.

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.

Deleterious Effect of Coronary Brachytherapy on Vasomotor Response to Exercise

BACKGROUND

Intracoronary radiotherapy (brachytherapy) has been proposed as treatment option for in-stent restenosis. Long-term results of brachytherapy with regard to vascular integrity and vasomotor responsiveness are unknown. The purpose of the present study was to determine the vasomotor response after brachytherapy and to assess its influence on vasomotion during exercise.

METHODS AND RESULTS

Biplane quantitative coronary angiography was performed at rest and during bicycle exercise in 27 patients with coronary artery disease. Fourteen patients underwent coronary stenting and were studied 10+/-3 months after intervention (control group). Thirteen patients were treated with brachytherapy (Guidant Galileo System) for in-stent restenosis with a mean dosis of 20 Gy at 1 mm into the vessel wall and were studied 9+/-1 months after radiation (brachytherapy group). Minimal luminal area, stent area, and proximal, distal, and a reference vessel area were determined. The reference vessel showed exercise-induced vasodilation (26+/-4%, P<0.001) in both groups. Vasomotion within the stented vessel segments was abolished. In control subjects, the proximal and distal segments showed exercise-induced vasodilation (17+/-2% and 22+/-7%, respectively; P<0.005). In contrast, there was exercise-induced vasoconstriction in the proximal and distal vessel segments of the brachytherapy group (-14+/-3% and -16+/-4%, respectively; P<0.01). Sublingual nitroglycerin was associated with maximal vasodilation of the proximal and distal vessel segments in both groups.

CONCLUSIONS

Normal vessel segments elicit flow-mediated vasodilation during exercise. Stent implantation does not affect physiological response to exercise proximal and distal to the stent. Brachytherapy eliminates exercise-induced vasodilation, although dilatory response to nitroglycerin is maintained, suggesting endothelial dysfunction as the underlying mechanism.

New strategies to prevent restenosis

The Holy Grail of cardiovascular pharmacology has been the search for an effective therapy targeting restenosis after angioplasty and/or intra-arterial stenting. The failure of promising therapeutics in clinical trials underscores the complexity and redundancy of the signaling cascades regulating mitogenesis and fibrogenesis. Novel therapeutic modalities have potential to target dysfunctional signaling elements directly in vascular smooth muscle cells. Significant progress in the treatment against restenosis will require the exploitation and cross-fertilization of developments in the fields of pharmacology, bioengineering, genetics, and molecular biology. Collaboration among researchers in these fields will be essential.

Intracoronary brachytherapy for the prevention of restenosis after percutaneous coronary revascularization

PURPOSE

The purpose of this article is to review the current literature pertaining to intracoronary brachytherapy for the prevention of restenosis after percutaneous coronary revascularization (PCR).

METHODS

English-language articles were identified through a MEDLINE search (January 1984 to January 2003) using the keywords brachytherapy, radioactive stents, and coronary arteries. In addition, pertinent reference citations from relevant articles were reviewed.

RESULTS

Restenosis after PCR is a complex process, thought to be due to a combination of vessel wall remodeling and neointimal proliferation. To date, catheter-based delivery of intracoronary brachytherapy has been found to prevent vessel wall remodeling and causes a reduction in the proliferation of the neointima. Neointimal proliferation, as measured by mean neointimal area, was reduced in all animal studies (range 26%-91%). In contrast, animal studies examining radioactive stents demonstrated an increase in neointimal proliferation, suggesting that they may not be helpful at preventing post-PCR restenosis. All human studies using catheter-based intracoronary brachytherapy for in-stent restenosis have employed either beta (beta) or gamma (gamma) radiation sources with variable doses of radiation (range 7-56 Grays [Gy]). Restenosis occurred in 12% to 40% of patients in nonrandomized studies, and clinical events occurred in 13% to 50% of patients. To date, there have been 7 published randomized trials in humans comparing catheter-based intracoronary brachytherapy to placebo, with a total of 1047 patients. The dose of radiation in the trials ranged from 14 Gy to 30 Gy. During follow-up, 8% to 33% of patients who received brachytherapy had restenosis versus 39% to 64% of patients receiving placebo. Clinical events occurred in 19% to 50% among patients who received brachytherapy versus 29% to 79% among patients receiving placebo. The majority of human studies examining radioactive stents do not demonstrate a reduction in restenosis in patients post-PCR. There are no randomized trials examining radioactive stents in humans.

CONCLUSION

Nonrandomized studies of radioactive stents suggest they are not effective at preventing in-stent restenosis. In contrast, data from animal and human studies suggest that catheter-based intracoronary brachytherapy can prevent in-stent restenosis and reduce clinical events post-PCR.

Catheter based intracoronary brachytherapy leads to increased platelet activation

BACKGROUND

Vascular brachytherapy (VBT) after percutaneous coronary intervention (PCI) is associated with a higher risk of stent thrombosis than conventional treatment.

OBJECTIVE

To investigate in vivo periprocedural platelet activation with and without VBT, and to assess a possible direct effect of radiation on platelet activation.

DESIGN

Of 50 patients with stable angina, 23 received VBT after PCI, while 27 had PCI only. The 23 patients who received VBT after PCI were pretreated for one month with aspirin and clopidogrel. Platelet activation was assessed by flow cytometry.

RESULTS

The two patient groups did not differ in their platelet activation before the intervention. There was a significant increase in activation immediately after VBT, with 21.2% (interquartile range 13.0% to 37.6%) thrombospondin positive and 54.0% (42.3% to 63.6%) CD 63 positive platelets compared with 12.7% (9.8% to 14.9%) thrombospondin positive and 37.9% (33.2% to 45.2%) CD 63 positive platelets before the intervention (p < 0.001 and p < 0.01, respectively). Patients without VBT had no periprocedural difference in platelet activation immediately after PCI. No increase in platelet activation was found after ex vivo irradiation of blood samples obtained from healthy controls.

CONCLUSIONS

Catheter based intracoronary VBT carried out according to current standards is highly thrombogenic. The current antithrombotic treatment with aspirin and clopidogrel is not sufficient to suppress platelet activation during the procedure. From in vitro experiments, it appears that platelet activation during brachytherapy is not caused by irradiation but by the procedure of catheter based VBT.

Successful brachytherapy of coronary vasospasm

Brachytherapy is a proposed treatment for in-stent restenosis and is the subject of several clinical trials and debates. The standard treatment of patients with variant angina is to eliminate vasoconstrictive factors and to administer vasodilating drugs. This is the first description of successful brachytherapy for coronary spasm.

Endovascular brachytherapy after percutaneous transluminal angioplasty of recurrent femoropopliteal obstructions

PURPOSE

To test the preventive effect of endovascular brachytherapy (EVBT) on restenosis following secondary angioplasty in patients with presumed neointimal restenosis in the femoropopliteal segment.

METHODS

From March 1997 through May 2000, 100 patients (58 men; mean age 70 years, range 45-87) with postangioplasty femoropopliteal segment restenoses were enrolled and randomized to treatment with repeat angioplasty and EVBT (n=51) or to angioplasty alone (n=49) as control. The groups were similar with regard to demographics and lesion characteristics. High-dose-rate EVBT was performed with (192)Ir irradiation without a centering device (12 Gy for a reference vessel radius of 3 mm and a 2-mm reference depth). Primary endpoint in the 1-year follow-up was recurrent obstruction >50% documented by duplex ultrasound; the secondary endpoint was clinical improvement.

RESULTS

Only 44 (86%) of 51 patients received adequate EVBT due to technical failure, so the 7 failures were included with the controls in the per-protocol adherence analysis. At 1 year, the patients receiving EVBT had a restenosis rate of 23% (10/44), which differed significantly (p<0.028) from the 42% (23/56) rate in controls. Clinical results tended to be better with EVBT, but differences did not achieve statistical significance.

CONCLUSIONS

EVBT without a centering device reduced restenosis significantly in patients with recurrent stenosis after angioplasty, which confirms previous results in primary long-segment femoropopliteal obstructions.

Cost-effectiveness of gamma radiation for treatment of in-stent restenosis: results from the Gamma-1 trial

BACKGROUND

Recently, several randomized trials have demonstrated that intracoronary brachytherapy can reduce the rates of both angiographic and clinical restenosis in patients undergoing percutaneous coronary intervention (PCI) for in-stent restenosis. Whether this practice is cost-effective is unknown.

METHODS AND RESULTS

Between December 1997 and July 1998, 252 patients with in-stent restenosis were randomized to receive brachytherapy or placebo after successful PCI as part of the Gamma-1 trial. We collected detailed resource utilization and cost data for each patient's initial hospitalization and for 1 year after randomization. Compared with conventional treatment, intracoronary brachytherapy increased procedure duration, physician services, and equipment costs. As a result, initial costs were increased by nearly $4100 per patient ($15 724 versus $11 675, P<0.001). Over the 1-year follow-up period, brachytherapy reduced the need for repeat revascularization by 21% and reduced the need for bypass surgery by 44%. Although follow-up medical care costs were $2200/patient lower with brachytherapy, total costs remained higher at 1 year ($28 543 versus $26 737, P=0.46). In a sensitivity analysis that incorporated recent technical modifications and the use of prolonged antiplatelet therapy to prevent late thrombotic occlusion, follow-up cost savings increased to $3600/patient, and 1-year costs were slightly lower with brachytherapy ($26 352 versus $26 729, P=0.87). Subgroup analysis demonstrated significant cost savings in patients with diabetes and patients who did not undergo repeat stenting.

CONCLUSIONS

As performed in the Gamma-1 trial, coronary brachytherapy for in-stent restenosis improved clinical outcomes but increased 1-year costs compared with standard therapy. If late thrombosis can be eliminated, however, this technology has the potential to reduce overall medical care costs.

Coronary in-stent restenosis: current status and future strategies

In-stent restenosis (ISR) is a novel pathobiologic process, histologically distinct from restenosis after balloon angioplasty and comprised largely of neointima formation. As percutaneous coronary intervention increasingly involves the use of stents, ISR is also becoming correspondingly more frequent. In this review, we examine the available studies of the histology and pathogenesis of ISR, with particular reference to porcine and other animal models. An overview of mechanical treatments is then provided, which includes PTCA, directional coronary atherectomy and high speed rotational atherectomy. Radiation-based therapies are discussed, including a summary of current problems associated with this modality of treatment. Finally, novel strategies for the prevention of ISR are addressed, including novel developments in stents and stent coatings, conventional drugs, nucleic acid-based drugs and gene transfer. Until recently, limited pharmacologic and mechanical treatment options have been available for both treatment and prevention of ISR. However, recent advances in gene modification and gene transfer therapies and, more particularly, in local stent-based drug delivery systems make it conceivable that the incidence of ISR will now be seriously challenged.

Targeting the adventitia with intracoronary beta-radiation: comparison of two dose prescriptions and the role of centering coronary arteries

PURPOSE

To compare by intravascular ultrasound (IVUS) the efficacy of delivering the prescribed dose to the adventitia between two commonly used dose prescriptions for intracoronary radiotherapy.

METHODS AND MATERIALS

In 59 human postangioplasty coronary vessels, one IVUS cross-section (1 mm thick) with the highest plaque burden was used for creating dose-volume histograms with different hypothetical positions of the source.

RESULTS

On average, prescription to 1 mm beyond lumen surface resulted in delivery of the prescribed dose (20 Gy +/- 20%) to a higher fraction of adventitial volume than with the prescription to 2 mm from the source, with source placed in vessel center, lumen center, or in the IVUS catheter position. Source placement in the lumen center resulted in a low dose heterogeneity to the adventitia and the least dose heterogeneity to the intima.

CONCLUSIONS

Prescription to 1 mm beyond lumen surface appeared more effective in delivering the prescribed dose to the adventitia than the American Association of Physicists in Medicine (AAPM) recommended prescription to 2 mm from the source center. Moreover, centering the source in the lumen provides the better balance of effective adventitial targeting and intimal dose homogeneity. Modification of the current AAPM recommendation for dose prescription for intracoronary radiotherapy should be considered.

Complete vascular healing and sustained suppression of neointimal thickening after local delivery of advanced c-myc antisense at six months follow-up in a rabbit balloon injury model

BACKGROUND

Neointimal hyperplasia following percutaneous transluminal coronary angioplasty (PTCA) is one of the major components of the process of restenosis. We evaluated the long-term impact of local delivery of c-myc neutrally charged antisense oligonucleotides (Resten-NG) upon neointimal formation following PTCA in a rabbit model.

METHODS

PTCA was performed in the iliac arteries of 10 New Zealand white rabbits at 8 atm for 30 s, three times. An infusion of 500 micro g Resten-NG (n=6) or saline (n=4) was delivered to the site at 2 atm via the outer balloon pores of the transport catheter over 2 min. The diet was supplemented with 0.25% cholesterol for 10 days before and 6 months following PTCA.

RESULTS

After 6 months, animals were sacrificed and vessels were fixed in formalin, processed and stained with hematoxylin, eosin, and movat. Histological analysis revealed complete vascular healing in both groups of animals. Planimetry showed that intimal areas were 1.71+/-0.25 and 0.65+/-0.36 mm2 in the control and antisense delivery groups, respectively (P<.05).

CONCLUSION

We conclude that local delivery of Resten-NG significantly inhibited neointimal thickening following PTCA in a rabbit for up to 6 months.

Will coronary artery surgery disappear in 10 years' time?

Over the past 20 years, percutaneous coronary intervention has progressively developed and matured, and many patients with severe coronary artery disease can now be revascularized non-surgically. So are the days of coronary artery bypass graft surgery numbered?

Effect of short pulsed nonablative infrared laser irradiation on vascular cells in vitro and neointimal hyperplasia in a rabbit balloon injury model

BACKGROUND

Neointimal hyperplasia after PTCA is an important component of restenosis.

METHODS AND RESULTS

Cultures of rabbit endothelial cells and smooth muscle cells (SMCs) were irradiated with different doses of nonablative infrared (1064-nm) radiation. Normalized viability index detected with nondestructive Alamar Blue assay and direct cell count were studied. Our experiments demonstrated dose-dependent cytostatic or cytotoxic effects of laser irradiation. We also evaluated the long-term effect of endoluminal nonablative infrared laser irradiation on neointimal hyperplasia in a rabbit balloon injury model. PTCA of both iliac arteries of 23 New Zealand White rabbits was performed. One iliac artery was subjected to intra-arterial subablative infrared irradiation via a diffuse tip fiber. The contralateral vessel served as control. The diet was supplemented with 0.25% cholesterol and 2% peanut oil for 10 days before and 60 days after PTCA. Morphometry after 60 days showed that intimal areas were 0.76+/-0.18 and 1.85+/-0.30 mm(2) in the laser and control arteries, respectively (P=2.2x10(-11)).

CONCLUSIONS

We conclude that nonablative infrared laser inhibited neointimal hyperplasia after PTCA in cholesterol-fed rabbits for up to 60 days.