In vivo intravascular laser photodynamic therapy in rabbit atherosclerotic lesions using a lateral direction fiber

Longer term assessment of photodynamic therapy for intimal hyperplasia: a pilot study

PURPOSE

To determine the potential long term (three or six months) effectiveness of photodynamic therapy (PDT) in reducing intimal hyperplasia in swine.

METHODS

Intimal hyperplasia in the abdominal aortae of swine was created by a combination of fat-supplemented diet and balloon catheter injury prior to PDT. Swine were randomly allocated into one of three groups which received either: (i) both drug and light (PDT), (ii) drug only, or (iii) light only. Twenty-four hours following administration of the photosensitizer PHOTOFRIN (porfimer sodium) at 2.5 mg/kg, two distinct 1 cm spots on the posterior wall of the abdominal aorta were illuminated by an argon pumped dye laser tuned to 630 nm for an energy fluence of 120 J/cm2. After three or six months, swine were sacrificed, perfusion fixed, and had their aortae removed for light and electron microscopy.

RESULTS

Intimal hyperplasia reduction following PDT persisted for the three or six months follow up period. Experimental vessels receiving PDT showed a 26.0+/-4.5% ( n = 2, ie. four spots) and 30.8+/-5.4% ( n = 1, ie. two spots) smaller percent intimal area after three or six months of recovery, respectively. Control groups receiving either light or drug only showed less than a 6% difference in percent intimal area. Medial and adventitial layers were unaffected in all groups. Electron microscopy demonstrated that the endothelium or endothelial-like cells had regenerated in both the posterior and adjacent areas of the abdominal aortae with no clear difference between them.

CONCLUSIONS

These findings suggest that PDT may be beneficial in reducing intimal hyperplasia for up to three or six months in swine.

A first trial in the clinical application of photodynamic therapy for the prevention of restenosis after coronary-stent placement

BACKGROUND AND OBJECTIVES

The aim of this clinical study was to evaluate the safety of local delivery of a photosensitizer followed by photodynamic therapy (PDT), to determine its effectiveness in reducing in-stent restenosis.

STUDY DESIGN/PATIENTS AND METHODS

Porfimer sodium was administered via a local delivery catheter to five coronary-stent implanted lesions followed by irradiation with a pulse laser. Coronary angiography (CAG) was performed at the baseline, after the procedure and at a 6-month follow-up.

RESULTS

By the 18-month clinical follow-up, no adverse events such as photodermatosis, or myocardial ischemia had occurred. At the follow-up, no coronary embolization, dissection, or aneurysmal dilatation was observed in the CAG. In-stent diameter stenosis, late loss, and loss index were 19.16+/-8.20%, 0.37+/-0.18 mm, and 0.19+/-0.12, respectively. No in-stent restenosis was observed.

CONCLUSIONS

This study suggests that PDT, with local delivery of Porfimer sodium, is safe and may be a feasible technique in preventing in-stent restenosis.

Clinical potential of photodynamic therapy in cardiovascular disorders

Atherosclerosis and intimal hyperplasia remain obstacles for surgeons to overcome following vascular reconstructions. Even with all of the technical improvements that have occurred in the past several decades, long term patency following intervention is hindered by these inherent adverse developments. Today, the use of light is seen as a potential treatment modality in vascular surgery. Photodynamic therapy (PDT) has been used in the treatment of cancer, and because of its continued success in vascular experimental models it is now being tested in clinical trials for vascular diseases. PDT offers the surgeon many advantages, and it may have unlimited uses in the clinical setting. Is PDT the ultimate treatment modality for the cardiovascular surgeon and will it help to overcome the inherent failures associated with vascular reconstructions? It may be too early to answer these questions, but with the current successes demonstrated by PDT, there is a need for further testing in clinical trials. In the near future, PDT may be used clinically as a treatment modality to inhibit restenosis and intimal hyperplasia following surgical intervention.

Photodynamic therapy for the prevention of intimal hyperplasia in balloon-injured rabbit arteries

This study was performed to demonstrate accumulation of the photosensitizer hematoporphyrin derivative (HPD) in atherosclerosis and to determine whether intimal hyperplasia, the main cause of restenosis after angioplasty, can be inhibited by photodynamic therapy (PDT). Forty Japanese White rabbits were subjected to balloon endothelial injury in the common iliac artery. Five groups of rabbits, ie, immediately after, or 3, 7, 14 or 28 days after the balloon injury, were injected with HPD. These rabbits were sacrificed 24h after HPD administration, and HPD fluorescence was investigated in the injured arteries by fluorescence microscopy. Other groups of rabbits were injected with HPD 24h before PDT, and they were then subjected to intravascular Hg-Xe flash-lamp irradiation immediately after (0D-PDT), or 3 days (3D-PDT), 7 days (7D-PDT), or 14 days (14D-PDT) after the balloon injury. All rabbits were sacrificed 28 days after the balloon injury, and histological sections of PDT-treated arteries were examined by light microscopy. Slight, uniform HPD accumulation was observed in the injured media immediately after the balloon injury, and throughout the entire media and the neointima on day 7. On day 14, HPD accumulation had diminished in the media and increased in the intima, and on day 28 no HPD remained in the media. In the 0D- or 3D-PDT groups, no inhibition of intimal hyperplasia was observed. In contrast, there was significant inhibition of intimal hyperplasia in the 7D- and 14D-PDT groups, and the most effective inhibition was in the 7D-PDT group. This study demonstrated that PDT with HPD inhibits smooth muscle cell growth and decreases the intimal hyperplasia response in rabbits.

Photodynamic therapy of atherosclerosis using YAG-OPO laser and Porfimer sodium, and comparison with using argon-dye laser

We performed photodynamic therapy (PDT) using the Yttrium Aluminium Garnet-Optical Parametric Oscillated (YAG-OPO) laser in cases of atherosclerosis, and examined its efficacy in vivo. We also performed PDT using an Argon-dye (Ar-dye) laser with the same output, and compared the efficacies. Following balloon denudation injury of the thoracoabdominal aorta, rabbits were raised on a cholesterol diet for 16 weeks, producing atheroma in that region. At 24 h following the administration of Photofrin 5 mg/kg, PDT was performed, and animals were sacrificed at 1 day, 1 week, and 2 weeks following the procedure to examine its efficacy. This was compared with the efficacy of PDT using the Ar-dye laser. Following PDT using a YAG-OPO laser, an increase in the vessel lumen was seen due to reduction of the hypertrophic intima and media, without the appearance of inflammatory cells. This result was seen more strongly in PDT using the pulse wave YAG-OPO laser than with the continuous wave Ar-dye laser, affecting not just the intima but also the media. These data demonstrated that PDT can effectively regress atherosclerotic lesions.

What does photodynamic therapy have to offer radiation oncologists (or their cancer patients)?

Major advances have recently been made in photodynamic therapy (PDT) for clinical application, including the development of more powerful photosensitizers and light sources and suitable light applicators. PDT is emerging as an attractive new form of cancer therapy, suitable for treating superficial lesions (less than 1 cm in depth) and carcinoma in situ, or as an adjuvant to surgery for more bulky disease. PDT is therefore complementary to radiotherapy which is better suited to treating larger tumours. There are some qualitative similarities between light distribution in tissue during superficial illumination and ionizing radiation dose distributions during external beam irradiation, or between interstitial PDT and brachytherapy, although the geometric scale is very different (visible light penetrates a maximum of 5-10 mm in tissue). The contribution of scattered light to tissue irradiance is much greater than for ionizing radiation and in situ light dosimetry is very important (although rather complicated) to ensure adequate illumination without over-treating. Dosimetry and treatment planning are highly advanced for ionizing radiation and are routine in all radiotherapy departments. Proper in situ light dosimetry and dose distribution calculation for PDT is in its infancy. Physicists have an important role to play in the further optimization of clinical PDT and much of the infrastructure and expertise present in the radiotherapy department is ideally suited to accommodate PDT. In this review, parallels and contrasts are made between PDT and ionizing radiation for both mechanistic and dosimetric aspects of the therapies. A summary of the most interesting clinical applications is also given.