Comparison of local intravascular drug-delivery catheter systems

Photodynamic therapy for the treatment of atherosclerotic plaque: Lost in translation?

Acute coronary syndrome is a life-threatening condition of utmost clinical importance, which, despite recent progress in the field, is still associated with high morbidity and mortality. Acute coronary syndrome results from a rupture or erosion of vulnerable atherosclerotic plaque with secondary platelet activation and thrombus formation, which leads to partial or complete luminal obstruction of a coronary artery. During the last decade, scientific evidence demonstrated that when an acute coronary event occurs, several nonculprit plaques are in a "vulnerable" state. Among the promising approaches, several investigations provided evidence of photodynamic therapy (PDT)-induced stabilization and regression of atherosclerotic plaque. Significant development of PDT strategies improved its therapeutic outcome. This review addresses PDT's pertinence and major problems/challenges toward its translation to a clinical reality.

Adventitial VEGF165 gene transfer prevents lumen loss through induction of positive arterial remodeling after PTCA in porcine coronary arteries

Negative arterial remodeling still plays an important role in the pathogenesis of coronary restenosis even in the era of interventional stenting (e.g. arterial narrowing occurs proximal and distal of a stented segment). Previous studies suggest that increased angiogenesis and inhibited regression of injury-induced adventitial microvessels prevents negative remodeling. We have examined the effect of local vascular endothelial growth factor (VEGF(165)) gene transfer on adventitial microvessel angiogenesis/regression and arterial remodeling after coronary angioplasty. Twenty pigs underwent angioplasty, each one in two major coronary arteries, followed by plasmid liposome gene transfer with either VEGF(165) or control gene LacZ (50 microg DNA with 50 microg of Lipofectine) into the (peri)adventitial space using a needle injection catheter. Arteries were examined at days 1, 7, 14, and 28. Local delivery of VEGF(165) gene into the outer compartments of balloon-injured porcine coronary arteries reduced lumen area loss due to distinct positive remodeling (arterial enlargement). Prevention of adventitial microvessel regression, enhanced adventitial elastin accumulation, reduced adventitial myofibroblast numbers, and a pronounced adventitial inflammatory response considered as a part of arterial healing seem to be the main VEGF-mediated mechanisms indicating the therapeutic potential of VEGF for restenosis prevention.

C-type natriuretic peptide for reduction of restenosis: gene transfer is superior over single peptide administration

BACKGROUND

Restenosis is still a significant clinical problem limiting the long-term therapeutic success following balloon dilation or stent implantation. New approaches are necessary inhibiting neointima formation and simultaneously promoting re-endothelialization. Therefore, long-term therapeutic effects of adventitial liposome-mediated C-type natriuretic protein (CNP) gene and CNP peptide applications in a porcine model for restenosis post-angioplasty were investigated.

METHODS

For in vitro applications, primary cultures of porcine vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) were used. Gene transfer was performed with cationic lipid DOCSPER [1,3-dioleoyloxy-2-(N5-carbamoylspermine)propane]. In vivo treatment of pig femoral arteries was adventitial using a needle injection catheter following balloon angioplasty. Arteries were investigated by angiography, Evan's blue staining, histomorphometry, immunohistochemistry, PCR and RT-PCR.

RESULTS

Using CNP gene transfer in vitro, 29.4+/-7.2% reduction of cell proliferation in VSMCs was observed. In ECs, the CNP gene did not compromise cellular growth. For the CNP peptide the optimal concentration was 1 mM with 50.7+/-11.3% reduction of VSMC proliferation and 12.1+/-5.3% enhancement of growth of ECs. Three weeks following application in vivo complete re-endothelialization was observed in all treated groups. At 3 months significant reduction of neointima formation was observed using CNP gene vs. CNP peptide (85.9+/-7.8% vs. 63.3+/-27.6% reduction, P<0.05) compared to control treatment.

CONCLUSION

Periadventitial liposome-mediated CNP gene transfer in vivo resulted in a significant long-term reduction of neointima formation without compromising endothelial repair and was superior over single CNP peptide administration. Advantages of CNP are its physiological origin and simultaneous inhibition of VSMC proliferation and promotion of EC growth.

C-type natriuretic peptide inhibits constrictive remodeling without compromising re-endothelialization in balloon-dilated renal arteries

PURPOSE

To investigate the long-term effect of local, liposome-mediated gene transfer of C-type natriuretic peptide (CNP) plasmid versus CNP protein on restenosis in porcine renal arteries following balloon angioplasty.

METHODS

The renal arteries of 15 pigs were dilated and the adventitia at the site of balloon injury injected with CNP protein, pCR3.1 plasmid encoding CNP, or the beta-galactosidase gene (control) via a needle injection catheter. Five animals receiving the CNP and control genes in dilated arteries were sacrificed after 3 weeks to analyze re-endothelialization, proliferation, and early CNP expression. Ten animals designated for the long-term experiments (3 months) were treated with the CNP gene versus CNP protein (n=3), the CNP gene versus the control gene (n=3), and the CNP protein versus the control gene (n=3). One animal served as a dilated non-treated control. Transfection and expression of CNP and beta-galactosidase were measured by polymerase chain reaction (PCR) and reverse transcription PCR. Renal arterial lumen narrowing was measured with angiography and histology. Endothelialization was assessed using Evans blue stain; vWF, CD31, factor VIII, and Ki67 were markers for immunohistochemical analysis.

RESULTS

An intact endothelial layer was seen at 3 weeks following angioplasty in all transfected arteries. Three months following treatment, computer-assisted morphometric analysis revealed significant enlargement of the arterial cross-sectional areas in CNP plasmid- treated vessels compared to dilated but untreated arteries (CNP plasmid +34.8%+/-13.9% versus CNP protein -1.75%+/-19.9% versus beta-galactosidase -47.0%+/-13.9%, p<0.01). Angiographic analysis showed significant enlargement of the arterial diameter compared to dilated, untreated arteries (CNP plasmid +20.8%+/-6.8% versus CNP protein +5.7%+/-6.0% versus beta-galactosidase -24.5%+/-10.2%, p<0.01).

CONCLUSIONS

Local application of CNP plasmid proved superior to CNP protein in producing rapid re-endothelialization and significantly enlarging the renal arterial lumen following dilation.

Novel percutaneous adventitial drug delivery system for regional vascular treatment

A novel intracoronary microsyringe system (MicroSyringe) was developed for regulated drug injection into the adventitial space. In this report, the feasibility, safety, and distribution pattern of vascular treatment with this modality were tested in 17 swine by delivering Oregon green-labeled paclitaxel (OGP) and tacrolimus. Coronaries were harvested 0.5-96 hr postinjection and analyzed for drug by fluorescence histochemistry (OGP) and liquid chromatography-mass spectrometry (tacrolimus). Histopathological analysis was subsequently performed. The microsyringe deliveries were performed safely in all cases. In the OGP-injected group, within 2 hr postprocedure there was intense staining of the adventitia, media, and endothelium around the injection site, and by 23 hr staining extended distally by 27.5 mm. With tacrolimus, similar longitudinal drug distribution was seen; furthermore, by 48 hr there was detectable drug over 40 mm proximal and distal to the injection site. Significant levels of tacrolimus were detectable in coronaries at 96 hr. Percutaneous adventitial delivery is safe, feasible, and provides consistent dosing for complete treatment of a vascular territory.

Long-term retention of a novel antioxidant sulphur-substituted fatty acid analogue after local delivery in porcine coronary arteries

OBJECTIVE

Antioxidants have been suggested to reduce restenosis after balloon angioplasty. A novel sulphur-containing fatty acid, tetradecylthioacetic acid (TTA), with antioxidant properties, is efficiently incorporated into cellular phospholipids. We have determined the uptake and retention of TTA after local coronary artery delivery in 20 pigs.

DESIGN

Radiolabelled TTA was delivered to 40 main coronary arteries via a multiporous coronary angioplasty balloon catheter inflated before, after, or without overstretch vessel injury. The animals were killed at intervals of up to 6 weeks post-procedure. The radioactivity of the tissue sections was determined as nmol TTA/g tissue.

RESULTS

Concentrations of TTA in the coronary arteries were 1.84 +/- 0.45 nmol/g up to 24 h, 1.50 +/- 0.96 nmol/g at 2 weeks, 0.22 +/- 0.11 nmol/g at 4 weeks and a trace was present at 6 weeks (p-value for trend <0.01). The arterial wall uptake at the delivery site was higher than distal to delivery (1.84 +/- 0.37 vs 0.55 +/- 0.13 nmol/g, p = 0.006) and perivascular fat (p < 0.01) but not higher than in the myocardium. Infusion before, after or without vessel injury was not important for tissue concentration.

CONCLUSIONS

After local coronary artery delivery, the antioxidant TTA is taken up by the arterial wall in which it is retained for at least 4 weeks.

Restenosis and gene therapy

Atherosclerosis is one of the main causes of mortality and morbidity in westernised countries. Treatment of symptomatic atherosclerosis by angioplasty involves major vascular responses such as neointima formation and constrictive vascular remodelling leading to restenosis. Stent placement prevents vasoconstriction but is associated with in-stent neointima formation. Therefore, stent placement requires adjunctive therapy. In this review we discuss the potential of local gene therapy for restenosis. More particularly, we focus on strategies to inhibit smooth muscle cell (SMC) proliferation and migration, prevent thrombosis, decrease oxidative stress in the arterial wall and enhance re-endothelialisation associated with adaptive remodelling. The potential of different vector systems and devices for local gene transfer in the arterial wall is discussed.

Prevention of Restenosis Using the Gene for Cecropin Complexed with DOCSPER Liposomes under Optimized Conditions

Up to 30% of patients undergoing coronary angioplasty develop a renarrowing of treated vessels following percutaneous transluminal coronary angioplasty with or without stent implantation, called restenosis. Smooth muscle cell proliferation, among other mechanisms, is an important factor in restenosis leading to neointima formation and consequent arterial lumen narrowing. Cecropins are antimicrobial peptides with antiproliferative properties in mammalian cells which have been shown to suppress neointimal formation. In this investigation, a plasmid carrying the gene for pre-pro-cecropin A, complexed with new generation liposomes optimized for transfer conditions for vascular cells was delivered to the adventitia of arteries in a porcine arterial injury model using a needle injection catheter. Retention of the plasmid in treated arteries was demonstrated for at least 21 days following delivery. Whereas previous experiments using first generation liposomes demonstrated significant but not complete neointima inhibition, the use of new liposomes under optimized conditions resulted in almost total suppression of neointimal proliferation. Thus, in vivo gene transfer of cecropins may be therapeutically applicable in restenosis prevention.

Quantification of horseradish peroxidase delivery into the arterial wall in vivo as a model of local drug treatment: comparison between a porous and a gel-coated balloon catheter

PURPOSE

To quantify horseradish peroxidase (HRP) delivery into the arterial wall, as a model of local drug delivery, and to compare two different percutaneous delivery balloons.

METHODS

Perforated and hydrophilic hydrogel-coated balloon catheters were used to deliver HRP in aqueous solution into the wall of porcine iliac arteries in vivo. HRP solutions of 1 mg/ml were used together with both perforated and hydrophilic hydrogel-coated balloon catheters and 40 mg/ml HRP solutions were used with the hydrogel-coated balloon only. The amount of HRP deposited in the arterial wall was then determined photospectrometrically.

RESULTS

Using the 1 mg/ml HRP solution, the hydrogel-coated balloon absorbed 0.047 mg HRP into the coating. Treatment with this balloon resulted in a mean vessel wall concentration of 7.4 microg HRP/g tissue +/- 93% (standard deviation) (n = 7). Treatment with the hydrogel-coated balloon that had absorbed 1.88 mg HRP into the coating (using the 40 mg/ml HRP solution) led to a mean vessel wall concentration of 69.5 microg HRP/g tissue +/- 74% (n = 7). Treatment with the perforated balloon using 1 mg/ml aqueous HRP solution led to a mean vessel wall concentration of 174 microg/g +/- 81% (n = 7). Differences between the hydrogel-coated and perforated balloons (1 mg/g solutions of HRP) and between hydrogel-coated balloons (0.047 mg vs 1.88 mg absorbed into the balloon coating) were significant (p < 0.05; two-sided Wilcoxon test).

CONCLUSIONS

The use of a perforated balloon catheter allowed the delivery of a higher total amount of HRP compared with the hydrogel-coated balloon, but at the cost of a higher systemic HRP application. To deliver 174 microg HRP per gram of vessel wall with the perforated balloon, 6.5 +/- 1.5 mg HRP were lost into the arterial blood (delivery efficiency range = 0.2%-0.3%). With 0.047 mg HRP loaded into the coating of the hydrogel balloon, 7.4 microg HRP could be applied to 1 g of vessel wall (delivery efficiency 1.7%), and with 1.88 mg HRP loaded into the coating of the hydrogel balloon, 69.5 microg HRP could be applied per gram of vessel wall (delivery efficiency 0.6%).

Local drug delivery: impact of pressure, substance characteristics, and stenting on drug transfer into the arterial wall

Injection parameters for local drug delivery are frequently determined by studies with marker substances. However, the pharmacologic properties of the actual drug may influence delivery efficiency and lead to different results. Aim of this study was to assess the delivery capacities of two device-drug combinations in order to verify this approach for further in vivo studies. Tritiated (3H) preparations (5 ml) of the hydrophylic low-molecular-weight heparin reviparin and the lipophilic taxane paclitaxel were injected into the left anterior descending artery of freshly explanted porcine hearts with the Infusasleeve II catheter system. A balloon support pressure of 6 atm and infusion pressures of 40, 60, 80, or 100 psi were used. In three additional groups, reviparin was injected following stent implantation and paclitaxel was injected prior to or following stent implantation. Arteries along with surrounding myocardium were harvested. The artery was carefully dissected, and artery and myocardium were separately homogenized, and activity was measured. Of the totally delivered activity, 0.09%+/-0.03% (40 psi) to 0.17%+/-0.13% (100 psi) of reviparin and 2.03%+/-0.67% (60 psi) to 2.68%+/-1.57% (100 psi) of paclitaxel were found in the vessel wall. The results for different injection pressures were not significantly different for either drug. The percentage activity delivered to the vessel wall was substantially larger in the paclitaxel group as compared to reviparin delivery (P < 0.01 at 60, 80, and 100 psi). The mean concentration of reviparin in the artery was 20 to 33 times higher than in the myocardium. For paclitaxel the factors were 110 to 243. Stent implantation prior to or following local delivery did not result in a different delivery efficiency. The results demonstrate that the characteristics of the delivered drug contribute largely to the delivery efficiency. Using identical injection parameters, drug concentrations in the arterial wall were significantly higher for the lipophilic paclitaxel as compared to the hydrophilic reviparin. Stenting of the artery did not influence delivery efficiency.

Needle injection catheter delivery of the gene for an antibacterial agent inhibits neointimal formation

Percutaneous transluminal coronary angioplasty is a routinely used non-surgical revascularization technique for patients with coronary artery disease. Up to 30% of patients undergoing coronary angioplasty develop a renarrowing of treated vessels, called restenosis. Smooth muscle cell proliferation is thought to be an important factor in restenosis; this leads to neointima formation and arterial lumen narrowing. Neointima may be reduced by the transfer of genes encoding proteins with antiproliferative effects. Cecropins are antimicrobial peptides with antiproliferative properties in mammalian cells. Cecropin A is one member of this family of peptides. In this article, a plasmid carrying the gene for the immature form, pre-pro-cecropin A, complexed with liposomes was locally delivered to perivascular tissue in a porcine arterial injury model using a needle injection catheter. Retention of the plasmid in the treated arteries was demonstrated at both 8 and 21 days following application. Transferred plasmid DNA was not detected in any other tissues analyzed. Pre-pro-cecropin A-specific transcripts could also be found in treated arteries. Balloon-injured vessels demonstrated significantly reduced neointima at 21 days in vessels treated with the pre-pro-cecropin A gene compared with neointimal area in those given a control gene (P < 0.05). The needle injection catheter appears to be useful for local intravascular gene delivery. In vivo gene transfer of cecropins may be of therapeutic relevance in restenosis prevention by limiting cell proliferation.

Fluorescence spectrum analysis of atherosclerotic plaque using doxycycline

Using doxycycline (DOXY), fluorescence spectrum analysis was performed on arteriosclerotic lesions, and the efficacy of this method was examined in basic and clinical studies. In the basic study, DOXY 50 mg was administered intravenously to arteriosclerotic rabbits, and the thoracoabdominal aorta removed. Fluorescence spectral analysis was performed on each specimen, and the fluorescence spectral pattern, peak intensity and degree of intimal hypertrophy were studied. In the clinical study, DOXY 200 mg was administered intravenously to 6 human subjects with stable angina and coronary arterial stenosis of greater than 90%, and coronary angiography, coronary angioscopy and fluorescence spectral analysis were performed. DOXY accumulation in the arteriosclerotic intima of rabbit aortae was confirmed. The fluorescence spectrum was monomodal, peaking at around 532 nm. In the noncalcification group, significant correlation was observed between peak intensity and arteriosclerotic intimal thickness. Using DOXY as a fluorescent marker, it was possible to assess the level of arteriosclerotic intimal hypertrophy. Clinically, it was possible to obtain the DOXY spectrum of the coronary arteries.

Endovascular manipulation to restrict restenosis

The processes that take place following damage to the vessel wall are well understood. Endovascular manipulation by its very nature induces such damage and the repair process can lead to a recurrence of symptoms. There have been many clinical trials of drugs chosen for their known impact on preventing excess vessel wall response. With one or two exceptions none of these trials has shown any benefit, partly because only low doses could be given systemically to avoid side effects. Local drug delivery allows high doses to be given where needed, at the site of the process, without inducing systemic complications. There are various drugs and agents that have been shown to be effective in models of vessel wall damage, including heparin, nitric oxide, inhibitors of platelet function and the antisense oligonucleotides. Some of these agents are now being tested in clinical trials. Methods of delivering the agent include devices that bathe the luminal layer, deliver the agent to the media or inject it into the adventitia where a reservoir can form. Stents improve the outcome after angioplasty, but can also induce a proliferative vessel wall response. To overcome this, stents have recently been considered as local delivery devices with radiation being delivered and polymer coated stents, loaded with agents, being developed. While local drug delivery provides great promise as a way of reducing the adverse effect of response of the vessel wall to damage, the results of clinical trials in humans are awaited.

Gene therapy for restenosis: getting nearer the heart of the matter

Intensive work over the past decade has been directed to the study of vascular gene transfer as an approach to the unresolved problem of restenosis. This effort has resulted in a significant foundation of knowledge relative to the activities of potentially therapeutic gene products as well as the capabilities and limitations of vector systems and mechanical delivery modalities available for effecting the vascular expression of these gene products. In several instances, significant progress has been made by experiments highlighting unexpected difficulties and the need for more comprehensive understanding. It is thus now possible to clearly define and address specific challenges that must be overcome in order to make feasible progress from the preclinical to the clinical arena. The key challenges at present appear to include the evolution of clinically practical delivery methods that meet the kinetic requirements of achieving efficient gene transduction and the availability of vectors that maximize efficiency while minimizing undesirable host responses. Emerging data suggest that approaches to solving each of these issues may have recently been developed. Basic research evaluating these new delivery mechanisms and molecular vectors is essential to establish their true potential for use in the clinical arena.

Chronic cannulation and fistulization procedures in swine: a review and recommendations

Swine are important animal models in biomedical research. Some experimental procedures may require chronic access to blood vessels, organs, and structures. Chronic access procedures may be utilized for collection of blood and body fluids as well as for the infusion of test substances. This manuscript reviews methodologies that have been reported to be effective for these procedures. It also makes recommendations on the maintenance of indwelling catheters, cannulas, and fistulas.

[Local drug delivery and gene therapy]

One of the most important problems in clinical cardiology is still unresolved, i.e., the development of a restenosis following coronary balloon angioplasty. Our knowledge about the sequelae of pathophysiologic events occurring during neointima formation is still far from complete (Figure 1) and numerous therapeutic trials using systemic administration of drugs with different mechanisms of action have failed. Possible innovative strategies are the local administration of high doses of drugs into the coronary arteries and local gene therapeutic interventions to inhibit neointima formation by reducing the proliferation of vascular smooth muscle cells. Numerous catheter devices were developed (Figure 2) in order to enable the local application of high doses of a drug or DNA. Additionally, galenic techniques are being developed to guarantee a steady release of locally administered drugs, e.g. from drug containing liposomes or microcarriers (Figure 3). There are already several animal models in which the development of a neointima was reduced by injecting antisense oligonucleotides directed towards the RNA encoding cell cycle regulatory proteins or peptides. Alternatively, the transfer of cDNA encoding proteins or protein products which inhibit the cellular proliferation and migration are being tested in vitro and in vivo with the help of reporter genes (Figure 4). Although, gene transfer techniques are believed to offer great therapeutic options for the future, the clinical data available today regarding this method are very limited and are derived from studies in patients with peripheral arterial disease. Thus, it is still questionable if gene transfer techniques will ever be able to become an integral part of our standard treatment for patients with vascular diseases.

Mural delivery of iloprost with use of hydrogel-coated balloon catheters suppresses local platelet aggregation

PURPOSE

To develop reproducible and quantifiable methods for mural delivery of iloprost, a potent agent against platelet aggregation, with use of hydrogel-coated angioplasty balloons, and to determine the in vivo effect of direct iloprost delivery on platelet aggregation at the angioplasty site.

MATERIALS AND METHODS

Drug loading of tritiated iloprost from an immersion solution onto hydrogel-coated balloons was evaluated as a function of balloon size (3 mm x 2 cm, 6 mm x 2 cm, 8 mm x 3 cm; n = 4 each), drug concentration (0.0715 mg/mL, 0.1072 mg/mL, 0.1430 mg/mL; n = 3 each), and duration of immersion (40 seconds, 60 seconds, 120 seconds; n = 3 each). In another set of experiments, optimal drying methods were tested to minimize drug loss within a protective delivery sheath (n = 3 each). Ex vivo angioplasty was performed on excised swine arteries to estimate how much of the drug present on the balloon could be delivered to the wall (n = 3 iliac segments). Finally, in vivo angioplasty was performed in three Yorkshire pigs (n = 6 iloprost-treated and 6 control arteries) and indium-111-labeled platelet aggregation was measured at these sites, which were harvested 1 hour after the procedure.

RESULTS

In the initial set of experiments, the authors found that the volume of drug loaded is determined by the wet-volume of the hydrogel coating, that the majority of volume loading occurs within the first 2 minutes, and that the volume uptake is independent of the drug concentration. The optimal drying method resulting in the least loss of iloprost within the sheath (only 4%) was prolonged drying (5 hours) under ambient conditions. Ex vivo angioplasty experiments showed that approximately 33% of the drug present on the balloon can be delivered to the wall. Finally, in vivo experiments showed that platelet aggregation is significantly suppressed at treated sites (by approximately 33% compared to control sites; P = .03) by minuscule mural doses of iloprost (roughly estimated at under 1 microg).

CONCLUSION

Quantifiable and reproducible methods for loading iloprost onto hydrogel-coated angioplasty balloons were developed. The best of these methods was able to deliver enough iloprost into the wall to significantly reduce local platelet aggregation.

Endovascular catheter-delivered photodynamic therapy in an experimental response to injury model

BACKGROUND

The effectiveness of local endovascular photodynamic therapy (PDT) in preventing tissue hyperplasia was evaluated in a vascular injury model.

METHODS

Standardized unidirectional arterial injury with a directional atherectomy catheter was performed in porcine arteries (n = 180). Animals (n = 72) were randomly allocated to unidirectional injury only (Group 1), injury followed by drug delivery of photosensitizer with a porous balloon (Group 2), or by local exposure to monochromatic light (Group 3). In Group 4, injury was followed by local drug delivery of photosensitizer and subsequent exposure to light (PDT). Up to 21 days after treatment, all experimental vessels were excised, fixed and processed for histology, immunohistochemistry and transmission electron microscopy.

RESULTS

After vascular injury an inflammatory and myoproliferative response was observed in Groups 1, 2 and 3 (mean tissue hyperplasia/media ratio 1.0 +/- 0.5 at 21 days; area tissue hyperplasia: 1.57 +/- 0.9 mm2). Proliferation in injured vascular segments (Group 1-3) reached a maximum at 7 days, with 6%. Only in Group 4, after injury followed by photodynamic therapy, was there no significant vascular response (mean tissue hyperplasia/media ratio 0.3 +/- 0.2: area tissue hyperplasia: 0.1 +/- 0.05 mm2 p < 0.001, proliferating cells 0.3%).

CONCLUSION

Vascular response after unidirectional injury was suppressed only by endovascular photodynamic therapy.

New applications in photodynamic therapy. Introduction

Photodynamic therapy is now recognized as a legitimate therapy for both palliative and potentially curative treatment of solid tumors. This represents a major achievement for investigators who have committed their careers to PDT. Scientific research characteristically runs well ahead of accepted views and technologies. This Symposium-in-Print perhaps provides a snapshot of the potential for this technology during the next two decades.

Local photodynamic therapy reduces tissue hyperplasia in an experimental restenosis model

Local photodynamic therapy may have potential in preventing myointimal hyperplasia after angioplasty. In this study, the effect of photodynamic therapy was evaluated in an experimental model of restenosis. Standardized unidirectional arterial injury with a directional atherectomy catheter was performed in porcine arteries. Animals were randomly allocated to four groups: group 1, unidirectional injury only; group 2, injury followed by local delivery of photosensitizer; group 3, injury followed by local exposure to monochromatic light; and group 4, where injury was followed by local drug delivery of photosensitizer and subsequent exposure to light (photodynamic therapy). Seven, 14 or 21 days after treatment, all experimental vessels were excised, fixed and processed for histology. An inflammatory and myoproliferative response was observed after injury in vessels from groups 1, 2 and 3. In group 4, after injury followed by photodynamic therapy, the myoproliferative response was significantly reduced. Thus, in this study, tissue hyperplasia after unidirectional injury was effectively suppressed by photodynamic therapy.