Photodynamic therapy in the normal rat colon with phthalocyanine sensitisation

Photodynamic and Photothermal Therapies: Synergy Opportunities for Nanomedicine

Tumoricidal photodynamic (PDT) and photothermal (PTT) therapies harness light to eliminate cancer cells with spatiotemporal precision by either generating reactive oxygen species or increasing temperature. Great strides have been made in understanding biological effects of PDT and PTT at the cellular, vascular and tumor microenvironmental levels, as well as translating both modalities in the clinic. Emerging evidence suggests that PDT and PTT may synergize due to their different mechanisms of action, and their nonoverlapping toxicity profiles make such combination potentially efficacious. Moreover, PDT/PTT combinations have gained momentum in recent years due to the development of multimodal nanoplatforms that simultaneously incorporate photodynamically- and photothermally active agents. In this review, we discuss how combining PDT and PTT can address the limitations of each modality alone and enhance treatment safety and efficacy. We provide an overview of recent literature featuring dual PDT/PTT nanoparticles and analyze the strengths and limitations of various nanoparticle design strategies. We also detail how treatment sequence and dose may affect cellular states, tumor pathophysiology and drug delivery, ultimately shaping the treatment response. Lastly, we analyze common experimental design pitfalls that complicate preclinical assessment of PDT/PTT combinations and propose rational guidelines to elucidate the mechanisms underlying PDT/PTT interactions.

Increasing cancer permeability by photodynamic priming: from microenvironment to mechanotransduction signaling

The dense cancer microenvironment is a significant barrier that limits the penetration of anticancer agents, thereby restraining the efficacy of molecular and nanoscale cancer therapeutics. Developing new strategies to enhance the permeability of cancer tissues is of major interest to overcome treatment resistance. Nonetheless, early strategies based on small molecule inhibitors or matrix-degrading enzymes have led to disappointing clinical outcomes by causing increased chemotherapy toxicity and promoting disease progression. In recent years, photodynamic therapy (PDT) has emerged as a novel approach to increase the permeability of cancer tissues. By producing excessive amounts of reactive oxygen species selectively in the cancer microenvironment, PDT increases the accumulation, penetration depth, and efficacy of chemotherapeutics. Importantly, the increased cancer permeability has not been associated to increased metastasis formation. In this review, we provide novel insights into the mechanisms by which this effect, called photodynamic priming, can increase cancer permeability without promoting cell migration and dissemination. This review demonstrates that PDT oxidizes and degrades extracellular matrix proteins, reduces the capacity of cancer cells to adhere to the altered matrix, and interferes with mechanotransduction pathways that promote cancer cell migration and differentiation. Significant knowledge gaps are identified regarding the involvement of critical signaling pathways, and to which extent these events are influenced by the complicated PDT dosimetry. Addressing these knowledge gaps will be vital to further develop PDT as an adjuvant approach to improve cancer permeability, demonstrate the safety and efficacy of this priming approach, and render more cancer patients eligible to receive life-extending treatments.

Photodynamic therapy in colorectal cancer treatment--The state of the art in preclinical research

BACKGROUND

Photodynamic therapy (PDT) is used in many different oncologic fields. Also in gastroenterology, where have been a few attempts to treat both the premalignant lesion and advanced colorectal cancer (CRC). This review aims to give a general overview of preclinical photodynamic studies related to CRC cells and animal studies of photodynamic effects related to CRC treatment to emphasize their potential in study of PDT mechanism, safety and efficiency to translate these results into clinical benefit in CRC treatment.

MATERIALS AND METHOD

Literature on in vitro preclinical photodynamic studies related to CRC cells and animal studies of photodynamic effects related to CRC treatment with the fallowing medical subject headings search terms: colorectal cancer, photodynamic therapy, photosensitizer(s), in vitro, cell culture(s), in vivo, animal experiment(s). The articles were selected by their relevance to the topic.

RESULTS

The majority of preclinical studies concerning possibility of PDT application in colon and rectal cancer is focused on phototoxic action of photosensitizers toward cultured colorectal tumor cells in vitro. The purposes of animal experiments are usually elucidation of mechanisms of observed photodynamic effects in scale of organism, estimation of PDT safety and efficiency and translation of these results into clinical benefit.

CONCLUDING REMARKS

In vitro photodynamic studies and animal experiments can be useful for studies of mechanisms and efficiency of photodynamic method as a start point on PDT clinical research. The primary disadvantage of in vitro experiments is a risk of over-interpretation of their results during extrapolation to the entire CRC.

Emergence of dual VEGF and PDGF antagonists in the treatment of exudative age-related macular degeneration

Neovascular ('wet') age-related macular degeneration (AMD) is the leading cause of blindness among Caucasians over the age of 55 in the USA and is an important cause of ocular morbidity worldwide. Progress in oncology, and more recently ophthalmology, led to the development of VEGF antagonists, three of which are now approved for the treatment of wet AMD. Recent discoveries in ophthalmology and vascular biology, however, suggest that combined inhibition of VEGF and platelet-derived growth factor (PDGF) may be more beneficial than inhibition of VEGF alone. Accordingly, numerous studies are underway to evaluate the role of anti-VEGF/PDGF combination therapies for the treatment of wet AMD. This review discusses the biology of VEGF and PDGF and current preclinical and clinical data exploring the use of combined VEGF/PDGF inhibitors in the treatment of neovascular age-related macular degeneration.

Phthalocyanine photophysics and photosensitizer efficiency on human embryonic lung fibroblasts

This study correlates the photophysical properties of aluminum phthalocyanine tetrasulfonate (AlPcTs), zinc phthalocyanine tetrasulfonate (ZnPcTs), and phthalocyanine tetrasulfonate (PcTs) with their ability to kill human embryonic lung (HEL) cells. Photofrin, a proven anti-cancer drug, was used for comparison. The photophysical properties include fluorescence emission spectra, fluorescence quantum yields, singlet state and radiative lifetimes, quantum yield for triplet formation, and fluorescence rate constants. Results indicate that photodynamic efficacy correlates inversely with fluorescence quantum yield and fluorescence lifetime and directly with quantum yield for triplet formation.

Photodynamic therapy using 5-aminolaevulinic acid for the treatment of dysplasia in Barrett's oesophagus

BACKGROUND

5-Aminolaevulinic acid (ALA) is the naturally occurring metabolic precursor of an endogenously formed photosensitiser, protoporphyrin IX. It is used topically to treat benign and malignant skin disorders by a process called photodynamic therapy (PDT). Recently, data are emerging on its systemic use in the treatment of dysplasia in Barrett's oesophagus.

OBJECTIVE

To investigate the use of ALA-PDT for the treatment of dysplasia and early cancer in Barrett's oesophagus.

METHODS

A systematic literature review and synopsis is given.

CONCLUSION

ALA is an attractive alternative to the currently approved photosensitiser (porfimer sodium) due to its oral route of administration, shorter generalised skin photosensitivity period and lower rate of stricture formation. The studies presented demonstrate that ALA-PDT is both safe and effective for the treatment of dysplasia and early cancer in Barrett's oesophagus.

Long-term experience with integral photodynamic therapy of TIS bladder carcinoma

Fifteen patients in whom superficial bladder tumours (TIS GII-III) recurred after the unsuccessful application of other treatments were treated by photodynamic therapy (PDT) and observed for 24-54 months. The results of therapy were evaluated by regular three-monthly check-ups (endoscopy, cytology, bladder mapping, renal ultrasonography) as well as by computed tomography (CT) examination at 8- to 13-month intervals. In nine patients treated by PDT no tumour recurrence has been found over the whole observation period. Two patients have remained free of tumour (12 and 14 months) after repeated transurethral resection (TUR) and Nd-YAG laser therapy after PDT. Two patients required a second application of PDT before the treatment goal was achieved. In one of these cases a circumscribed dysplasia which appeared at the left ostium 26 months after PDT was treated by TUR and Nd-YAG laser. Further observations showed it had been successfully removed. In six patients slight mucosal atypia persisted for at least 2.5 years. In the short-term course of further cases (n = 12) one cystectomy has to be performed because of bladder shrinkage. According to these preliminary results, PDT (with strict patient selection--worst-case situation with recommended cystectomy) is justified for recurrent superficial TIS bladder carcinoma.

Fractionated Illumination Significantly Improves the Response of Superficial Basal Cell Carcinoma to Aminolevulinic Acid Photodynamic Therapy

Photodynamic therapy (PDT) of superficial basal cell carcinoma (sBCC) using topical 5-aminolevulinic acid (ALA) and a light fluence of 75-100 J cm(-2) yields unsatisfactory long-term results. In several animal models, illumination with two light fractions 2 hours apart was considerably more effective than single illumination. Response is further enhanced if the fluence of the first light fraction is reduced, although the cumulative fluence is maintained. We compared the response of sBCC to a single illumination and 2-fold illumination scheme in which two light fractions of 20 and 80 J cm(-2) are performed 4 and 6 hours after the application of a single dose of 20% ALA. We randomly assigned 154 patients with a total of 505 primary sBCC into two treatment groups. Two hundred and forty-three lesions were treated using a single illumination of 75 J cm(-2) at a fluence rate of 50 mW cm(-2). Fractionated PDT, at the same fluence rate, was performed on 262 lesions. The complete response (CR) following a 2-fold illumination scheme is significantly greater than that following a single light fraction (P=0.002, log-rank test). Twelve months after therapy, CR rate to a 2-fold illumination is 97%, whereas the CR to a single illumination is 89%.

Comparing and combining light dose fractionation and iron chelation to enhance experimental photodynamic therapy with aminolevulinic acid

BACKGROUND AND OBJECTIVES

Enhancement of photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) has been demonstrated experimentally using light dose fractionation or CP94 iron chelation. This study extends this research.

STUDY DESIGN/MATERIALS AND METHODS

In normal rat colon, CP94 administration and light dose fractionation were independently and concurrently employed to enhance ALA-PDT. In colonic rat tumors, the most successful enhancement regimes were employed separately.

RESULTS

Independent use of light dose fractionation and iron chelation produced similar results in normal colon (2.4- and 2.9-fold more necrosis than controls, respectively). Using both techniques simultaneously produced fivefold enhancement. In the colonic tumors, light dose fractionation and iron chelation (using different parameters) produced two and five times the volume of necrosis, respectively.

CONCLUSIONS

Both techniques significantly enhanced ALA-PDT in the normal and neoplastic tissues investigated and produced similar levels of enhancement when comparable parameters were employed. Concurrent use of light dose fractionation and iron chelation in normal colon produced considerably more enhancement than either technique could achieve independently.

Photodynamic therapy with WST09 (Tookad): quantitative studies in normal colon and transplanted tumours

Photodynamic therapy (PDT) is attracting increasing interest for the safe destruction of localised tumours in a range of organs. However, most photosensitising drugs require a delay of hours to days between drug administration and light activation with skin photosensitivity that may last for weeks. WST09 (Tookad) is a new faster acting photosensitiser that clears within a few hours. In normal rat colon, after sensitisation with an intravenous bolus of WST09, light was delivered to a single point on the mucosa and the extent of PDT necrosis measured 3 days later. The lesion diameter was greatest with the highest dose of drug and light and the shortest drug light interval (DLI), falling rapidly with a DLI more than 5 min. In tumours transplanted subcutaneously or into the colon, the extent of necrosis only started falling with a DLI greater than 15 min, suggesting a possible window for tumour selectivity. Histological changes 3 days after PDT were essentially the same as those seen with longer acting photosensitisers. The lesion dimensions were comparable to the largest ones seen with other photosensitisers under similar experimental conditions. We conclude that WST09 is a powerful photosensitiser that produces PDT effects similar to those seen with longer acting drugs, but with the major advantages of a short DLI and rapid clearance.

The vascular response to photodynamic therapy with ATX-S10Na(II) in the normal rat colon

The mechanism of tissue damage from photodynamic therapy (PDT) may be cellular, vascular or both, depending on the photosensitising agent and the treatment conditions. Well established photosensitisers like porfimer sodium have an optimum drug light interval of two days and may cause skin photosensitivity lasting several weeks. ATX-S10Na(II) is a new photosensitiser that remains largely in the vasculature after systemic administration and clears from the body within a few hours. The present study looks at the factors controlling the extent of PDT necrosis using ATX-S10Na(II) and correlates these with changes in the circulation after PDT. Normal Wistar rats were sensitised with ATX-S10Na(II), 2 mg/kg. At laparotomy, a laser fibre was positioned just touching the colonic mucosa and 50 J light at 670 nm delivered varying the drug light interval (0.5-24 h) and light delivery regime (100 mW continuous, 20 mW continuous or 100 mW in five fractions). Some animals were killed at three days to document the area of necrosis, others received fluorescein shortly prior to death (from a few minutes to three days after PDT) to outline the zone of PDT induced vascular shutdown. Maximum necrosis was seen with the shortest drug light interval (0.5 h), with no effect by 6 h. Fractionating the light or lowering the power did not increase the necrosis. The area of fluorescein exclusion increased over the first 2 h after PDT (in contrast to the re-perfusion seen with other photosensitisers) and correlated with the area of necrosis. PDT with ATX-S10Na(II) is most effective with a drug light interval of less than one hour. It induces irreversible vascular shutdown that extends after completion of light delivery and which is largely independent of the light delivery regime.

Collagen secretion after photodynamic therapy versus scar-inducing anti-cancer modalities: an in vitro study

Photodynamic therapy (PDT) has been associated anecdotally with good quality healing and an absence of scar formation. Our previous studies, examining the levels of the collagen specific molecular chaperone Hsp47, have noted differences in the response after photodynamic therapy and hyperthermia at both the transcriptional and translational levels. In the present study the levels of Hsp47 after exposure to two chemotherapeutic agents (bleomycin and mitomycin). ionising radiation, hyperthermia and haematoporphyrin ester (HpE) mediated PDT were compared in both mouse and human fibroblast cell lines. A rapid assay for soluble collagen has also been used to quantify soluble collagen levels at early time points after treatment. Peak Hsp47 levels were found to correlate well with peak collagen levels. The results show that the levels of collagen measured in vitro are elevated in modalities associated with scarring in vivo but not after HpE-PDT.

Photodynamic effects on rabbit auricular veins after photosensitization with porfimer sodium: Implications of the results with respect to the treatment of esophageal varices with photodynamic therapy

BACKGROUND

There are numerous clinical applications for photodynamic therapy in the GI tract. The principal reason for the wide variety of lesions amenable to photodynamic therapy is the ability to treat large areas of mucosa without the need for complete visualization. This report describes observed hemodynamic and histologic changes in rabbit auricles after photodynamic therapy and the feasibility of photodynamic therapy for esophageal varices.

METHODS

Porfimer sodium and an argon-dye laser (630 nm, 300 mW/cm(2)) were used. Twenty rabbits were grouped according to porfimer sodium dose: group 1 (2.0 mg/kg, n = 10); group 2 (1.0 mg/kg, n = 6); group 3 (0.2 mg/kg, n = 4). Rabbit auricular veins were classified according to time duration of laser illumination: V(0), no illumination; V(5), 5 minutes; V(10), 10 minutes; V(15), 15 minutes. Hemodynamic changes were observed with a laser Doppler blood flow meter. Histologic changes were evaluated by light microscopy.

RESULTS

For groups 1 and 2, there was a significant decrease in blood flow for V(15) after photodynamic therapy, but not in group 3. There was a significant difference in the grade of thrombus between V(5) and V(15) in groups 1 and 2, and between V(10) and V(15) in group 2. There was a significant difference in the grade of venous dilation (congestion) for V(15) between groups 1 and 3 (p < 0.05, Kruskal-Wallis test).

CONCLUSIONS

Endoscopic photodynamic therapy could possibly improve the outcome for endoscopic treatment of esophageal varices beyond that achieved by sclerotherapy or band ligation alone.

Effects of photodynamic therapy on the absorption properties of disulphonated aluminum phthalocyanine in tumor-bearing mice

Time-resolved reflectance spectroscopy was performed on tumor-bearing mice, administered with disulphonated aluminum phthalocyanine (AlS(2)Pc, 5 mg/kg body weight), before, during and after photodynamic therapy. This allowed us to evaluate the absorption spectrum of AlS(2)Pc in vivo from 610 to 700 nm, and to investigate how the therapeutic irradiation affects it. Two tumor locations (intraderma on the back and intramuscular in the leg), and two uptake times (3 and 12 h) were considered. As already observed previously, the absorption spectrum of AlS(2)Pc in vivo is centered at 680-685 nm. The irradiation causes a blue-shift of the measured line shape, more or less marked depending on the experimental conditions. A reduction in absorption is also often observed upon illumination with therapeutic light doses.

Photodynamic therapy and the alimentary tract

Photodynamic therapy offers the possibility of relatively selective tumour necrosis and normal tissue healing. It has many potential applications but as yet no clear role. Articles, editorials and case reports published primarily in English and listed in Medline/ISI up to April 2000 or identified by a manual search have been reviewed in an attempt to provide a comprehensive overview of the use of photodynamic therapy in the alimentary tract. It is concluded that photodynamic therapy can be an effective treatment for superficial pre-malignant mucosal lesions and early cancers, especially in diffuse disease. Suitable patients include those wishing to avoid surgery, high risk subjects or those in whom other forms of treatment have failed. Superiority over other methods of ablation has not so far been demonstrated. Cheaper and more effective photosensitizers and improved techniques of light delivery are likely to increase the application of photodynamic therapy.

Oxygen monitoring during 5-aminolaevulinic acid induced photodynamic therapy in normal rat colon. Comparison of continuous and fractionated light regimes

Currently, the clinical use of 5-aminolaevulinic acid (ALA) induced protoporphyrin IX (PPIX) for photodynamic therapy (PDT) is limited by the maximum tolerated oral ALA dose (60 mg/kg). Attempts have been made to enhance this treatment modality without increasing the administered dose of ALA. One way to do this is through light dose fractionation, where the irradiation is interrupted at a particular point for a short period of time. This can produce up to three times more necrosis than with the same light dose delivered without a break. An oxygen microelectrode was employed to study the effect of continuous and fractionated light regimes on the level of oxygen in the colon of normal Wistar rats during ALA PDT. A rapid decline in pO2 occurred close to the irradiation fibre as soon as the light dose commenced. With the fractionated regime, a partial recovery in pO2 was observed during the dark interval which was reversed soon after the second light fraction commenced. We have shown that the level of tissue oxygen at the treatment site is affected differently when the light dose is fractionated, than when continuous illumination is employed. This factor may at least partially explain the difference in outcome of these two treatment regimes. Further, oxygen measurements might prove to be a useful way of monitoring PDT treatments if they can predict whether tissue is likely to be viable following treatment.

Current concepts in gastrointestinal photodynamic therapy

OBJECTIVE

To review current concepts of photodynamic therapy (PDT) applied to the treatment of tumors of the gastrointestinal tract.

SUMMARY BACKGROUND DATA

PDT initially involves the uptake or production of a photosensitive compound by tumor cells. Subsequent activation of the photoreactive compound by a specific wavelength of light results in cell death, either directly or as a result of vascular compromise and/or apoptosis.

METHODS

The authors selectively review current concepts relating to photosensitization, photoactivation, time of PDT application, tissue selectivity, sites of photodynamic action, PDT effects on normal tissue, limitations of PDT, toxicity of photosensitizers, application of principles of PDT to tumor detection, and current applications of PDT to tumors of the gastrointestinal tract.

RESULTS

PDT is clearly effective for small cancers, but it is not yet clear in which cases such treatment is more effective than other currently acceptable approaches. The major side effect of PDT is cutaneous photosensitization. The major limitation of PDT is depth of tumor kill. As data from current and future clinical trials become available, a clearer perspective of where PDT fits in the treatment of cancers will be gained. Many issues regarding pharmacokinetic data of photosensitizers, newer technology involved in light sources, optimal treatment regimens that take advantage of the pharmacophysiology of photoablation, and light dosimetry still require solution. One can foresee application of differing sensitizers and light sources depending on the specific clinical situation. As technologic advances occur, interstitial PDT may have significant application.

CONCLUSIONS

PDT has a potentially important role either as a primary or adjuvant mode of treatment of tumors of the gastrointestinal tract.

Fine-needle interstitial photodynamic therapy of the lung parenchyma: photosensitizer distribution and morphologic effects of treatment

STUDY OBJECTIVE

To look at the effect of interstitial photodynamic therapy (PDT) in normal lung parenchyma to assess its potential for treating localized, peripheral lung tumors.

DESIGN

Studies were performed on normal Wistar rats using the photosensitizer meso-tetrahydroxyphenyl chlorine. Drug distribution was measured by fluorescence microscopy on tissue sections. Light was delivered to the lungs via a single fiber inserted percutaneously under x-ray control and the PDT effect studied in animals killed at times up to 6 months later.

RESULTS

Fluorescence studies showed that the drug was initially distributed throughout the lung, but was later predominantly in the vasculature, bronchi, and macrophages. PDT produced sharply defined zones of hemorrhagic necrosis up to 12 mm in diameter that healed with regeneration of bronchial epithelium and local fibrosis. Different histologic effects were seen between drug light intervals of 1 and 3 days. Treatment was well tolerated, there was a low incidence of pneumothorax, and as long as the fiber tip was within the lung parenchyma, there was no damage to adjacent tissues.

CONCLUSION

Interstitial PDT produces zones of necrosis in normal lung that heal safely by a percutaneous technique without affecting adjacent areas of untreated lung. If the lesion size can be increased by using multiple fibers, this could be a promising new technique for treating localized, peripheral lung cancers in patients who are unfit for surgery.

Induction of apoptotic cell death by photodynamic therapy in human keratinocytes

The use of photodynamic therapy (PDT) for the treatment of skin and oral cancer has been the subject of several clinical studies but there has been little scientific evaluation of its mechanism of action. Evidence to date suggests that whilst epithelial cell death may be secondary to vascular damage, direct cell killing may occur and may involve an apoptosis-like mechanism. To investigate the mechanism of epithelial cell death following PDT, two cell lines, human epidermal keratinocytes (UP) and oral squamous cell carcinoma-derived cells (H376) were subjected to PDT with aluminium disulphonated phthalocyanine (AlS2Pc) as the photosensitizer and red laser light at 675 nm. Control groups received red laser light, photosensitizer or neither. The effects of PDT were assessed using an MTS cell-proliferation assay, which showed a significant reduction in viability (p < 0.01) for PDT-treated cells compared to controls. For morphological analysis, cells were stained with haemotoxylin and eosin and the numbers showing typical apoptotic features counted. The treated cultures showed significantly increased numbers of apoptotic cells. Moreover, the H376 control cultures showed a baseline level of apoptosis of approx. 15%. Apoptosis was confirmed by ultrastructural analysis and by in situ end-labeling of DNA fragments. The results show that PDT using AlS2Pc as a photosensitizer promotes apoptotic cell death in UP and H376 cells in vitro and suggest that direct killing of epithelial cells may contribute to tumour necrosis in vivo.

Photodynamic therapy inactivates extracellular matrix-basic fibroblast growth factor: insights to its effect on the vascular wall

PURPOSE

Photodynamic therapy (PDT), the light activation of photosensitizer dyes for the production of oxygen and other free radical moieties without the generation of heat, has been shown to inhibit the development of experimentally induced intimal hyperplasia. The host response to PDT, a form of vascular injury that results in complete vascular wall cell eradication, is devoid of inflammation and proliferation and promotes favorable vascular wall healing. These effects do not result in intimal hyperplasia and are suggestive of PDT-induced changes in the extracellular matrix (ECM). As a model to better understand the biologic consequences of PDT on the vascular wall matrix proteins, the effect of PDT was studied on the powerful matrix-resident mitogen basic fibroblast factor (bFGF) in vitro.

METHODS

PDT (5 to 200 J/cm2, 100 mW/cm2, 675 nm) was used with the photosensitizer chloroaluminum sulfonated phthalocyanine (5 micrograms/ml) to inactivate bFGF in vitro while 100 J/cm2 of irradiation was administered 24 hours after 5 mg/ml of the photosensitizer was used in vivo. PDT was used on bFGF in solution and on endothelial cell-derived ECM. Enzyme-linked immunosorbent assay was used to quantitate bFGF in solution after PDT treatment or after extraction from the ECM by collagenase and heparin. Functional activity of matrix-associated bFGF was assessed by smooth muscle cell mitogenesis by 3H-thymidine incorporation. To demonstrate the in vivo relevance of these observations, immunohistochemical analysis of PDT-treated rat carotid arteries was undertaken.

RESULTS

PDT eliminated detectable levels of bFGF in solution. PDT of ECM significantly reduced matrix-bound bFGF (1.0 +/- 0.6 vs 27.5 +/- 1.3 pg/ml; p < 0.0001). This reduction in bFGF after PDT of the ECM was associated with a decrease in vascular smooth muscle cell mitogenesis (52.4% +/- 4.6%; p < 0.0001) when plated on PDT-treated matrix compared with nontreated matrix. Quantitative replenishment of exogenous bFGF to PDT-treated matrix restored proliferation to baseline levels. PDT of rat carotid arteries demonstrated a loss of bFGF staining compared with control nontreated arteries.

CONCLUSIONS

PDT inactivation of matrix-resident bFGF and possibly other bioactive molecules can provide a mechanism by which PDT suppresses smooth muscle cell proliferation in the vessel wall. This free radical-mediated alteration of matrix may contribute to favorable vascular healing when PDT is used for the inhibition of injury-induced intimal hyperplasia.

Protoporphyrin-IX distribution and photodynamic effect in rat oesophagus after aminolaevulinic acid administration

BACKGROUND

Photodynamic therapy (PDT) is a method for local and selective tumour destruction achieved by the action of light on a photosensitizing drug.

METHODS

We investigated the distribution of 5-amino-laevulinic acid (ALA)-induced protoporphyrin-IX fluorescence in rat oesophagus by fluorescence microscopic examination and then studied the effects of PDT.

RESULTS

The highest level of fluorescence was achieved in the mucosa after 4 h of 300 mg/kg ALA administration. A clear difference in fluorescence between mucosa and muscularis was found in all samples except those taken 24 h after ALA administration. PDT with ALA caused destruction of the mucosal and, partly, submucosal layers of the oesophagus without damaging the muscularis layer.

CONCLUSIONS

According to our results with microscopic fluorescence kinetics and the preliminary results of PDT, selective destruction of the superficial layer of the rat oesophagus is achieved with PDT after ALA administration.

Photodynamic therapy: an effective, but non-selective treatment for superficial cancers of the oral cavity

It has often been claimed that photodynamic therapy (PDT) produces selective destruction of small cancers without affecting the adjacent normal tissue. The objective of our work was to treat small cancers of the oral cavity with PDT and subsequently excise the treated areas for histological studies of tumour and adjacent normal tissue exposed to the same light dose. Eleven patients with histologically proven T1NO oral squamous-cell carcinomas were treated with PDT, using Photofrin as a sensitiser. The tumours plus a surrounding cuff of normal tissue were exposed to 50 J/cm2 non-thermal laser light at 630 nm delivered by surface illumination and the treated areas subsequently excised. Histological staining and image analysis were used to determine the nature and extent of injury. No macroscopic distinction was evident between tumour and normal tissue exposed to light. Histologically, replacement of superficial epithelium, tumour and connective tissue with a fibrinous necrotic slough was seen. There was also loss of endothelium from small vessels, with haemorrhage and thrombosis. Preservation of subepithelial collagen and elastin was demonstrated with EVG staining. No evidence of selective tumour necrosis was found. Although depth of injury was variable, full thickness mucosal necrosis occurred in all cases.

The biology of photodynamic therapy

The subcellular, cellular and tissue/tumour interactions with non-toxic photosensitizing chemicals plus non-thermal visible light (photodynamic therapy (PDT) are reviewed. The extent to which endothelium/vasculature is the primary target is discussed, and the biochemical opportunities for manipulating outcome highlighted. The nature of tumour destruction by PDT lends itself to imaging outcome by MRI and PET.

Side effects and photosensitization of human tissues after aminolevulinic acid

Aminolevulinic acid (ALA) is being used as a "prodrug" for photodynamic therapy. The side effects of ALA have been only anecdotally reported and these effects as well as pharmacokinetics of the photosensitizing end product of ALA, protoporphyrin IX (PpIX), in patients undergoing operation are unknown. This study systematically determines the side effects of ALA and pharmacokinetics of PpIX in patients undergoing abdominal surgery. Patients were given 30 or 60 mg/kg ALA preoperatively, kept in subdued light for 48 hr, and monitored clinically and with laboratory tests for 5 to 7 days and for at least 2 months thereafter. Periodic plasma samples and tissue biopsies were analyzed for PpIX concentrations using a photodiode array system. No patient developed symptoms of porphyria other than nausea and vomiting, which occurred in 20%. Nearly one-quarter of patients developed transient abnormal liver functions. No patient developed cutaneous phototoxicity, abnormal neurologic function, or unexpected postoperative laboratory tests. The times of peak plasma, skin, skeletal muscle, omental, mucosal, muscularis mucosal, and tumor concentrations of PpIX varied among patients. In general, PpIX concentrations were significantly greater with the higher dose of ALA. Tumor PpIX concentrations were significantly greater than in other tissues except liver. In conclusion, ALA, up to 60 mg/kg, is associated with minimal side effects in patients undergoing operation. Actual tissue concentrations of PpIX suggest that endogenous photosensitization using systemically administered ALA is a mode of PDT feasible for treatment of adenocarcinomas of the gastrointestinal tract in humans.

Photodynamic eradication of amelanotic melanoma of the hamster with fast acting photosensitizers

Three porphycenes with fast pharmacokinetics were tested for their ability to photosensitize amelanotic hamster melanoma A-Mel-3 at short time intervals after injection. Laser light irradiation was performed at the time of maximal photosensitizer level in tumor tissue. Photodynamic therapy as short as 5 min after injection led to complete local tumor remission at a dosage of 1.4 mumol/kg for the porphycene CBPn. In comparison, Photofrin required 8.4 mumol/kg for local tumor remission in 5 of 6 animals with 24 hr accumulation time after injection. We propose a swift photodynamic protocol which can compete favorably with conventional techniques of tumor treatment.

Ex-vivo treatment of gastric Helicobacter infection by photodynamic therapy

Attempts to develop PDT for eradication of Helicobacter infection have only been successful in vitro. We have investigated the effect of topical sensitization (except ALA) of Helicobacter mustelae on explanted ferret gastric mucosa using one of five sensitizers (methylene blue (MB), toluidine blue O (TBO), phthalocyanine, haematoporphyrin derivative and 5-aminolavulinic acid), followed by irradiation with an appropriately tuned copper vapour pumped dye laser. A 90% reduction in counts of bacteria sensitized with 0.75 mg TBO kg-1 were seen after irradiation with 200 J cm-2. Concentrations of MB of 0.75 mg kg-1 and 7.5 mg kg-1 were not toxic to H. mustelae, but the further addition of 20 J cm-2 laser light reduced colony counts by more than 99%. MB at a concentration of 75 mg kg-1 exhibited significant dark toxicity towards H. mustelae, but further addition of 20 J cm-2 laser light resulted in near eradication of all colonies. The remaining three compounds were ineffective. Finally, we studied the microscopic fluorescence distribution of MB (7.5 mg kg-1) on ferret gastric mucosa after topical administration. Fluorescence was greatest in the superficial mucosal layer, upon which lies the bacteria. However, from experiments on rats, the energy required to kill the sensitized bacteria was insufficient to damage the underlying mucosa. We conclude that Helicobacter can be killed on host mucosal epithelium following topical administration of MB and subsequent exposure to laser light.

Mucosal ablation using photodynamic therapy for the treatment of dysplasia: an experimental study in the normal rat stomach

Surgery is the only effective treatment for dysplasia in the gastrointestinal tract with considerable associated morbidity and mortality and is difficult to justify without confirmed malignancy. Photodynamic therapy (PDT) produces localised necrosis, which can be limited to the mucosa. This study examined the mechanical properties of the normal rat stomach after PDT. The aim of this study was to measure the bursting pressure of PDT lesions in the stomach and to assess gastric emptying after producing circumferential mucosal necrosis at the pylorus by PDT. Two photosensitising agents were used--5-aminolaevulinic acid (ALA), and aluminium disulphonated phthalocyanine (A1S2Pc). Normal rats were sensitised and PDT lesions created in the stomach with red light. The bursting pressure was measured and compared with that in thermal control lesions. In further experiments, circumferential mucosal necrosis was produced at the pylorus, and animals observed for subsequent eating and weight gain. It was found that gastric bursting pressure was reduced after thermal injury, but not at any time after PDT (with A1S2Pc, but not ALA, adhesive omental reinforcement was required to maintain the gastric wall strength at one week). For the pyloric lesions, gastric emptying was permanently impaired using A1S2Pc, but with low dose ALA (20 mg/kg) had returned to normal by three days. With ALA, but not A1S2Pc, necrosis could be limited to the mucosa. In conclusion, using ALA, selective ablation of the gastric mucosa is possible, which does not reduce the strength of the stomach and only temporarily delays gastric emptying. PDT is a promising technique for the circumferential ablation of dysplastic mucosa.

Enhancement of photodynamic therapy with 5-aminolaevulinic acid-induced porphyrin photosensitisation in normal rat colon by threshold and light fractionation studies

5-Aminolaevulinic acid (ALA)-induced prophyrin photosensitisation is an attractive option for photodynamic therapy (PDT) since skin photosensitivity is limited to 1-2 days. However, early clinical results on colon tumours using the maximum tolerated oral dose of 60 mg kg-1 showed only superficial necrosis, presumably owing to insufficient intratumoral porphyrin levels, although inadequate light dosimetry may also be a factor. We undertook experiments using ALA, 25-400 mg kg-1 intravenously, to establish the threshold doses required for a PDT effect. Laser light at 630 nm (100 mW, 10-200 J) was delivered to a single site in the colon of photosensitised normal Wistar rats at laparotomy. The animals were killed 3 days later and the area of PDT-induced necrosis measured. No lesion was seen with 25 mg kg-1. The lesion size increased with larger ALA doses and with the light dose but little benefit was seen from increasing the ALA dose above 200 mg kg-1 or the light dose above 100 J. Thus there is a fairly narrow window for optimum doses of drug and light. Further experiments showed that the PDT effect can be markedly enhanced by fractionating the light dose. A series of animals was sensitized with 200 mg kg-1 ALA and then treated with 25 J. With continuous irradiation, the lesion area was 13 mm2, but with a single interruption of 150 s the area rose to 94 mm2 with the same total energy. Results were basically similar for different intervals between fractions (10-900 s) and different numbers of fractions (2-25). This suggests that a single short interruption in the light irradiation may dramatically reduce the net light dose required to achieve extensive necrosis.

Intraperitoneal photodynamic therapy in the rat: comparison of toxicity profiles for photofrin and MTHPC

Toxicity studies for intraperitoneal photodynamic therapy (IPPDT) were performed in Wag/RijA rats, using specially designed light delivery blocks for proper light distribution and light dosimetry. A recently developed photosensitizer mesotetrahydroxyphenylchlorin (mTHPC), excited at 652-nm wave-length, was compared with Photofrin (630 nm). Toxicity profiles for various sensitizer doses, light fluences and time intervals were investigated. A light fluence of 15 J.cm-2 delivered to the entire peritoneum 24 hr after 5 mg Photofrin per kg i.v. induced reversible impairment of intestinal, liver and kidney function. A dose of 0.2 mg mTHPC per kg i.v. followed by 6 J.cm-2 at 72 hr appeared to be equitoxic to the intestines; however, functional tests revealed little effect for this mTHPC-mediated IPPDT regime on liver or kidney. Histology demonstrated focal irreversible damage to the kidneys for both photosensitizers, not reflected in functional impairment. Light doses of 25 to 30 J.cm-2 at 24 hr after Photofrin or 8-12 J.cm-2, 72 hr after mTHPC caused lethal toxicity in the first 2 weeks due to intestinal damage. Higher light doses caused a shock syndrome and rhabdomyolysis resulting in death within 20 hr for both photosensitizers. In conclusion, maximum tolerable schedules for whole-abdomen IPPDT were defined for Photofrin and mTHPC. Both photosensitizers caused similar toxicity profiles depending on drug dose, light fluence and time interval.

Photodynamic therapy using 5-aminolaevulinic acid for experimental pancreatic cancer--prolonged animal survival

Experimental studies have been carried out using 5-aminolaevulinic acid (ALA) to induce transient porphyrin photosensitisation for photodynamic therapy (PDT) in a pancreatic cancer model in Syrian golden hamsters. ALA was given either intravenously or orally (in bolus or fractionated doses) with the laser light delivered by means of a bare fibre touching the tissue surface or external irradiation using a light-integrating cylindrical applicator. Animals were killed 1-24 h after ALA administration for pharmacokinetic studies and 3-7 days after light exposure to study PDT-induced necrosis. A separate survival study was also performed after a fractionated oral dose of ALA and external irradiation. Protoporphyrin IX sensitisation in the tumour tissue as measured by quantitative fluorescence microscopy was highest after intravenous administration of 200 mg kg-1 ALA and then in decreasing order after oral fractionated and oral bolus doses (both 400 mg kg-1). Laser light application at 630 nm to give 12-50 J from the bare fibre or 50 J cm-2 using surface illumination with the cylindrical applicator resulted in tumour necrosis up to 8 mm in depth. In larger tumours a rim of viable tumour was observed on the side opposite to illumination. In a randomised study, survival of treated animals was significantly longer than in the untreated control group (log-rank test, P < 0.02), although all animals died of recurrent tumour. This technique shows promise in the treatment of small volumes of tumour in the pancreas.

Photodynamic therapy of malignant and premalignant lesions in patients with 'field cancerization' of the oral cavity

The management of patients with 'field cancerization' of the oral mucosa, with multicentric foci of invasion, presents a considerable problem for the head and neck surgeon. Surgical resection of synchronous or metachronous primary squamous cell carcinomas, along with adjacent premalignant lesions, is likely to be associated with considerable mutilation. Photodynamic therapy (PDT) has been shown to be of value in the treatment of superficial tumours in the upper aerodigestive tract, with excellent healing of treated areas. This study reports the use of PDT to treat 11 patients with 'field cancerization' occurring in the oral cavity. Six patients had multiple primary cancers and five had single primary tumours. All had associated areas of leukoplakia. Each received Photofrin 2 mg/kg 48 hours prior to photoirradiation with 50-100 J/cm2 red laser light by surface illumination. Six to eight weeks later treated areas in 10 of the 11 patients showed a complete response to PDT; one patient had areas of residual leukoplakia. Two patients developed further areas of leukoplakia or erythroplakia within 12 months but no patient has had evidence of recurrent invasive carcinoma in the treated areas. Longer term follow-up will be necessary to exclude further recurrence. It is concluded that PDT offers an effective repeatable treatment option, whether on its own or as an adjunct to local excision, for patients with 'field cancerization' of the oral cavity.

Effects of photodynamic therapy in the normal mouse tongue

The effects of photodynamic therapy (PDT) on the normal mouse tongue were investigated. After using various doses (2.5, 10, and 20 mg/kg body wt) of the photosensitizing drug hematoporphyrin oligomers and 90 or 180 J/cm2 red light (630-nm) emitted from a pulsed neodymium:yttrium-aluminum-garnet dye laser was used to activate it 3 or 24 hours later. It was found that the 20-mg/kg dose elicited a severe response that included extensive vesicular and edema formation. A less severe response was observed with 10 mg/kg of the drug and low-power light (5 mJ/cm2/pulse) periodically delivered (1 hour interval between two 30-minute photoradiations). Such a regimen, however, produced more damage when compared with the higher power (15 mJ/cm2), continuous light delivery counterpart. Healing, except for the protocol with only a 3-hour drug-light interval, was attained by 5 days post-PDT as indicated by regeneration with histologically normal tissues and quantitatively a return to untreated, control values for cross-sectional areas and number of blood vessels. Bromodeoxyuridine immunohistochemistry disclosed an immediate increase in the labeling indices, ie, the percentage of S phase cycling cells, indicating stimulated cell proliferation secondary to repair and fast repopulation of the epithelium. Under the commonly used protocols, PDT was provided safely to the mouse tongue. The regimen of low drug dose and low power of light periodically delivered appears to be the most acceptable method. These parameter-dependent results may partly form the basis for the judicious application of PDT to the oral cavity.

Photodynamic therapy of oral cancer: photosensitisation with systemic aminolaevulinic acid

Photodynamic therapy with intravenous photosensitising drugs has been shown to be effective in the ablation of superficial cancers, but long-lasting photosensitivity is a serious disadvantage. Similar photosensitivity is a feature of certain types of porphyria. We present the first report of tumour necrosis brought about by photodynamic activation of a temporary endogenous porphyrin accumulation, after an oral dose of the haem precursor, 5-aminolaevulinic acid. In 4 patients, quantitative fluorescence microscopy showed that accumulation of the photoactive intermediate protoporphyrin IX peaked after 4-6 h in 4 oral cavity squamous cell carcinomas, returning to background in 24 h. Irradiation with non-thermal red laser light caused tumour necrosis in 3 patients.

Interstitial photodynamic therapy. Clinical experience with diffusing fibres in the treatment of cutaneous and subcutaneous tumours

Interstitial photodynamic therapy has a number of potential advantages over superficial treatment. We have treated 50 subcutaneous and cutaneous tumours interstitially, in nine patients. An additional 22 tumours in the same patients, were treated by superficial PDT. Patients received 1.5-2.0 mg kg-1 of polyhaematoporphyrin and 72 h later underwent treatment using a copper vapour dye laser producing red light at 630 nm. All interstitial treatments were delivered using cylindrical diffusing fibres and a wide range of light doses (5-1500 J cm-3). The complete response rate for all tumours treated interstitially was 52%, rising to 81% in those patients who received 2.0 mg kg-1 PHP and light doses in excess of 500 J cm-3. The overall incidence of skin necrosis was 32% and was 79% in those treated with light doses of greater than 500 J cm-3. The incidence of skin necrosis with interstitial PDT is lower than that seen with superficial photodynamic therapy but higher volumetric light doses are required to produce tumour complete responses. All treatments were well tolerated and volumes of tumour up to 60 cm3 were successfully treated. The penetration depth of 630 nm light in human breast cancer tissue was determined as 4 mm. Little true tumour tissue selectivity was detected by analysis of porphyrin levels in biopsy material.

Experimental studies to assess the potential of photodynamic therapy for the treatment of bronchial carcinomas

BACKGROUND

Photodynamic therapy (PDT) is a technique for producing localised tissue necrosis with light after prior administration of a photosensitising drug. There is some selectivity of uptake of photosensitisers in malignant tissue, although this is difficult to exploit. Full thickness necrosis in normal and neoplastic colon heals without perforation because of a lack of effect on collagen, making local cure a possibility. The experiments described here aim to establish whether these conclusions are also valid for bronchial tumours.

METHODS

In pharmacokinetic studies normal rats were given 5 mg/kg of the photosensitiser aluminium sulphonated phthalocyanine (A1SPc) intravenously and killed up to one month later. The distribution of A1SPc in the trachea was measured by chemical extraction and fluorescence microscopy. In subsequent experiments sensitised animals were treated with light delivered to the tracheal mucosa through a thin flexible fibre and the resultant lesions were studied for their size, mechanical strength, and healing. A series of resected human bronchial carcinomas were examined histologically for their collagen content.

RESULTS

The tracheal concentration of A1SPc in normal rats was maximum 1-20 hours after administration. Fluorescence microscopy revealed that most was in the perichondrium and submucosal stroma, with little in the cartilage. Light exposure showed necrosis of the soft tissues which healed by regeneration, but no effect on cartilage and no reduction in the mechanical strength of the trachea at any stage. Histological examination of resected human bronchial carcinomas showed more collagen in the tumour areas than would be found in normal regions.

CONCLUSIONS

PDT leads to necrosis of the soft tissues of the normal trachea but there is complete healing by regeneration, no risk of perforation (due to collagen preservation), and no effect on cartilage. Human bronchial carcinomas apparently contain more collagen than normal bronchi which may give protection against perforation following necrosis induced by PDT. PDT may have a role in eradicating small volumes of tumour tissue in situ and could be valuable for treating (1) small carcinomas in patients unfit for resection, (2) tumour remaining after surgical resection, (3) stump recurrences, or (4) to prolong palliation of tumours after debulking with the NdYAG laser.

The uptake of porphyrin and zinc-metalloporphyrin by the primate prostate

The relative distribution of sensitizer drugs in the prostate and its contiguous organs is of importance in the treatment of localized prostatic cancer with photodynamic therapy. Using the primate model, whose prostate is both morphologically and physiologically homologous with its human counterpart, the distribution of hematoporphyrin derivative (HpD) amongst organs of urological interest was determined. Hematoporphyrin derivative levels were comparatively low in both caudal and cranial prostatic lobes (0.93-1.77 micrograms/g) and were similar to those in rectum, urethra and the skin. The reticuloendothelial organs, liver, spleen and also the kidney accumulated the highest quantities of porphyrin (4.76-9.8 micrograms/g, liver > spleen > kidney). Despite a high avidity of prostatic tissue for zinc, a zinc-metalloporphyrin (Zn-HpD) did not concentrate selectively in the prostate. The results are of clinical value in view of the homology between the primate and the human.

Intra-abdominal photodynamic therapy: from theory to feasibility

Photodynamic therapy is a new anticancer technique, directed at the selective destruction of neoplastic tissue, which has been used in the treatment of superficial or intraluminal lesions. The technique has now reached the stage where it can be considered in the peroperative management of gastrointestinal tumours, for example in an attempt to eradicate micrometastases in the tissue around the primary tumour or in residual lymph nodes after curative resection. Many practical problems remain to be solved, such as the pharmacokinetics of photosensitizers, the dosimetry of illumination and the sensitivity of intra-abdominal organs. An experimental and clinical evaluation is in progress to assess the feasibility of photodynamic therapy in surgical practice.

Photodynamic therapy of the normal rat stomach: a comparative study between di-sulphonated aluminium phthalocyanine and 5-aminolaevulinic acid

Dysplasia in the upper gastrointestinal tract carries a risk of invasive malignant change. Surgical excision of the affected organ is the only treatment available. Photodynamic therapy has been shown to be promising in the treatment of early and superficial tumours and may be useful for the ablation of dysplastic mucosa. Because of the diffuse nature of the disease, such treatment would necessarily involve destruction of large areas of mucosa and it is desirable to confine its effect to the mucosa in order that safe healing can take place. By means of photometric fluorescence microscopy, we have studied the pattern of photosensitisation in the normal rat stomach using di-sulphonated aluminium phthalocyanine (AlS2Pc) and 5-aminolaevulinic acid (ALA) as photosensitisizers. AlS2Pc resulted in a panmural photosensitisation of the gastric wall with the highest level encountered in the submucosa. The mucosa and muscularis propria were sensitised to equal extent. Following light exposure, a full thickness damage resulted. ALA is a natural porphyrin precursor and exogenous administration gave rise to accumulation of protoporphyrin IX (PPIX) in the cells. The resultant pattern of photosensitisation was predominantly mucosal and its photodynamic effect was essentially confined to the mucosa. ALA produced a selective photosensitisation of the gastric mucosa for its photodynamic ablation with sparing the underlying tissue layers.

Fluorescence distribution and photodynamic effect of ALA-induced PP IX in the DMH rat colonic tumour model

Aminolaevulinic acid (ALA) is the first committed step in haem synthesis. In the presence of excess ALA the natural regulatory feedback system is disrupted allowing accumulation of protoporphyrin IX (PP IX) the last intermediate product before haem, and an effective sensitiser. This method of endogenous photosensitisation of cells has been exploited for photodynamic therapy (PDT). We have studied the fluorescence distribution and biological effect of induced PP IX in normal and tumour tissue in the rat colon. Fluorescence in normal colonic tissue was at a peak of 4 h with a rapid fall off by 6 h. The fluorescence had returned to background levels by 24 h. All normal tissue layers followed the same fluorescence profile but the mucosa showed fluorescent levels six times higher than the submucosa, with muscle barely above background values. At 6 h the ratio of fluorescence levels between normal mucosa and viable tumour was approximately 1:6. At this time laser treatment showed necrosis of normal mucosa and tumour with sparing of normal muscle. There was good correlation between the fluorescence distribution and the biological effect of ALA-induced photosensitisation on exposure to red light. ALA may be superior to conventional sensitisers for tumours that produce haem as the PP IX is synthesised in malignant cells while the other sensitisers mainly localise to the vascular stroma of tumours. There is also a greater concentration difference between the PP IX levels in tumours and in normal mucosa and normal muscle than with the other photosensitisers raising the possibility of more selective necrosis in tumours.