Distribution and photodynamic effect of disulphonated aluminium phthalocyanine in the pancreas and adjacent tissues in the Syrian golden hamster

Photodynamic Stromal Depletion in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest solid malignancies, with a five-year survival of less than 10%. The resistance of the disease and the associated lack of therapeutic response is attributed primarily to its dense, fibrotic stroma, which acts as a barrier to drug perfusion and permits tumour survival and invasion. As clinical trials of chemotherapy (CT), radiotherapy (RT), and targeted agents have not been successful, improving the survival rate in unresectable PDAC remains an urgent clinical need. Photodynamic stromal depletion (PSD) is a recent approach that uses visible or near-infrared light to destroy the desmoplastic tissue. Preclinical evidence suggests this can resensitise tumour cells to subsequent therapies whilst averting the tumorigenic effects of tumour-stromal cell interactions. So far, the pre-clinical studies have suggested that PDT can successfully mediate the destruction of various stromal elements without increasing the aggressiveness of the tumour. However, the complexity of this interplay, including the combined tumour promoting and suppressing effects, poses unknowns for the clinical application of photodynamic stromal depletion in PDAC.

Photodynamic Therapy for Pancreatic Ductal Adenocarcinoma

Simple Summary

Pancreatic ductal adenocarcinoma (PDAC) is among the most lethal of human cancers. Numerous clinical trials evaluating various combinations of chemotherapy and targeted agents and radiotherapy have failed to provide meaningful improvements in survival. A growing number of studies however have indicated that photodynamic therapy (PDT) may be a viable approach for treatment of some pancreatic tumors. PDT, which uses light to activate a photosensitizing agent in target tissue, has seen widespread adoption primarily for dermatological and other applications where superficial light delivery is relatively straightforward. Advances in fiber optic light delivery and dosimetry however have been leveraged to enable PDT even for challenging internal sites, including the pancreas. The aim of this article is to help inform future directions by reviewing relevant literature on the basic science, current clinical status, and potential challenges in the development of PDT as a treatment for PDAC.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is among the most lethal of human cancers. Clinical trials of various chemotherapy, radiotherapy, targeted agents and combination strategies have generally failed to provide meaningful improvement in survival for patients with unresectable disease. Photodynamic therapy (PDT) is a photochemistry-based approach that enables selective cell killing using tumor-localizing agents activated by visible or near-infrared light. In recent years, clinical studies have demonstrated the technical feasibility of PDT for patients with locally advanced PDAC while a growing body of preclinical literature has shown that PDT can overcome drug resistance and target problematic and aggressive disease. Emerging evidence also suggests the ability of PDT to target PDAC stroma, which is known to act as both a barrier to drug delivery and a tumor-promoting signaling partner. Here, we review the literature which indicates an emergent role of PDT in clinical management of PDAC, including the potential for combination with other targeted agents and RNA medicine.

Photodynamic therapy for cancer of the pancreas – The story so far

Pancreatic cancer has long been a leading cause of cancer death. Few patients are suitable for surgery and for those who are not, the response to treatment is generally poor. No more than about 10% survive for more than a year. Recent research has focused on focal treatment for local disease control. This review covers the development of one of the most promising options, photodynamic therapy (PDT).

This review covers pre-clinical and clinical studies. Laboratory work was designed to understand the effect of PDT on the normal pancreas and surrounding tissues and on transplanted cancers in the hamster pancreas to ensure safety prior to clinical application. Essentially all clinical studies have been undertaken in University College Hospital, London. Phase-I studies used the photosensitisers mTHPC and verteporfin in patients with localised but inoperable cancers.

Laboratory results showed that normal pancreas, bile duct, liver, stomach and major blood vessels could tolerate PDT without any unacceptable effects on the structure and function of these organs. Necrosis that healed safely was documented in transplanted cancers. The clinical trials showed that focal necrosis could be produced in inoperable cancers with acceptable levels of complications, but considerable refinements of treatment delivery and monitoring are required before the technique will be ready for assessment in controlled clinical trials.

PDT is showing promise for the minimally invasive treatment of localised pancreatic cancers, but it is still at an early stage of development. Much more work will be necessary to optimise techniques for applying PDT to these cancers and for combining it with other therapeutic options such as chemotherapy.

Photodynamic therapy for pancreatic cancer

OBJECTIVES

This study examined the status of photodynamic therapy (PDT) in the treatment of cancers of the pancreas.

METHODS

Original and review articles, editorials, and case reports published primarily in English and listed in Medline/ISI up to October 2006 or identified by a manual search have been reviewed in an attempt to provide a comprehensive overview of the mechanisms of PDT action and clinical application of PDT in the treatment of pancreatic cancers.

RESULTS

Photodynamic therapy represents a novel treatment of pancreatic malignancy; it produces local necrosis of tissue with light after administration of a photosensitizing agent. Evidences from in vivo and in vitro results have shown that PDT significantly decreases pancreatic cancer cell growth, destroys pancreatic carcinoma, and prolongs the survival of patients with unresectable pancreatic malignancy, and also show that PDT has disadvantages and limitations for the treatment of pancreatic cancer.

CONCLUSIONS

Photodynamic therapy can be an effective treatment of patients with pancreatic cancer, but more extensive preclinical and clinical trials are needed for further improvement in the clinical application of PDT, especially in avoidance of complications during PDT.

Photodynamic therapy using verteporfin photosensitization in the pancreas and surrounding tissues in the Syrian golden hamster

BACKGROUND/AIM

Photodynamic therapy (PDT) is a potential treatment for locally advanced pancreatic cancer. We aimed to assess the safety of interstitial PDT using verteporfin (benzoporphyrin derivative monoacid A - a novel photosensitizer with a short drug-light interval and limited cutaneous photosensitivity) in the Syrian golden hamster, and compare it to meso-tetrahydroxyphenylchlorin (mTHPC) which we have previously evaluated in preclinical and clinical studies.

METHODS

Verteporfin (2 mg/kg) was administered at laparotomy by inferior vena caval injection (n = 57), with plasma levels quantified at 5, 15, 30, 60 and 240 min, and 24 h. 15 min after photosensitization, tissues (liver, pancreas, duodenum, colon, aorta) were illuminated with 690 nm red laser light (150 mW), at a range of light doses (1-100 J/cm(2)). The PDT effects on the targeted organ and adjacent structures were assessed at post-mortem on days 3 and 21, or at the time of death.

RESULTS

The elimination half-life of verteporfin was 4-5 h. Light doses of 10, 25 and 50 J/cm(2) were safe in the hamster pancreas, liver and colon, respectively, and produced coagulative necrotic lesions of 3 (range 3-4), 10 (9-10) and 7 (7-8) mm diameter. Collagen was resistant to damage and lesions healed mainly by regeneration of normal tissue. At higher light doses, necrosis extended to the edge of organs, sometimes causing sealed duodenal perforations as seen with mTHPC.

CONCLUSION

The safety profile of verteporfin is very similar to mTHPC, with the advantages of a shorter drug-light interval and drug elimination time. Phase I clinical studies using this photosensitizer in pancreatic cancer should be feasible.

Photodynamic therapy for pancreatic and biliary tract carcinoma

The prognosis of patients with pancreatic and biliary tract cancer treated with conventional therapies such as stent insertion or chemotherapy is often poor, and new approaches are urgently needed. Surgery is the only curative treatment but is appropriate in less than 20% of cases, and even then it is associated with a 5-yr survival of less than 30% in selected series. Photodynamic therapy represents a novel treatment for pancreaticobiliary malignancy. It is a way of producing localized tissue necrosis with light, most conveniently from a low-power, red laser, after prior administration of a photosensitizing agent, thereby initiating a non-thermal cytotoxic effect and tissue necrosis. This review outlines the mechanisms of action of photodynamic therapy including direct cell death, vascular injury, and immune system activation, and summarizes the results of preclinical and clinical studies of photodynamic therapy for pancreaticobiliary malignancy.

Assessment of photosensitizer dosimetry and tissue damage assay for photodynamic therapy in advanced-stage tumors

Photodynamic therapy (PDT) efficacy is a complex function of tissue sensitivity, photosensitizer (PS) uptake, tissue oxygen concentration, delivered light dose and some other parameters. To better understand the mechanisms and optimization of PDT treatment, we assessed two techniques for quantifying tissue PS concentration and two methods for quantifying pathological tumor damage. The two methods used to determine tissue PS concentration kinetic were in vivo fluorescence probe and ex vivo chemical extraction. Both methods show that the highest tumor to normal tissue PS uptake ratio appears 4 h after PS administration. Two different histopathologic techniques were used to quantify tumor and normal tissue damage. A planimetry assessment of regional tumor necrosis demonstrated a linear relationship with increasing light dose. However, in large murine tumors this finding was complicated by the presence of significant spontaneous necrosis. A second method (densitometry) assessed cell death by nuclear size and density. With some exceptions the densitometry method generally supported the planimetry results. Although the densitometry method is potentially more accurate, it has greater potential subjectivity. Finally, our research suggests that the tools or methods we are studying for quantifying PS levels and tissue damage are necessary for the understanding of PDT effect and therapeutic ratio in experimental in vivo tumor research.

EUS-guided photodynamic therapy of the pancreas: a pilot study

BACKGROUND

Photodynamic therapy of pancreatic cancer by using percutaneously placed light catheters has been reported. The feasibility and safety of EUS-guided photodynamic therapy of the pancreas was studied in a porcine model.

METHODS

After injection of porfimer sodium, a 19-gauge needle was inserted into the pancreas, the liver, the spleen, and the kidney under EUS guidance. A small diameter quartz optical fiber was passed through the EUS needle and used to illuminate the tissue with laser light. The tissue response to photodynamic therapy was examined.

RESULTS

Localized tissue necrosis was achieved in all organs, without significant complication. There was no significant difference in inflammation induced by photodynamic therapy within the various organs.

CONCLUSIONS

EUS-guided photodynamic therapy is a safe and simple technique that can induce small areas of focal tissue ablation within the liver, the pancreas, the kidney, and the spleen, and potentially could be used to treat a variety of benign and malignant conditions.

Photodynamic therapy for cancer of the pancreas

BACKGROUND

Few pancreatic cancers are suitable for surgery and few respond to chemoradiation. Photodynamic therapy produces local necrosis of tissue with light after prior administration of a photosensitising agent, and in experimental studies can be tolerated by the pancreas and surrounding normal tissue.

AIMS

To undertake a phase I study of photodynamic therapy for cancer of the pancreas.

PATIENTS

Sixteen patients with inoperable adenocarcinomas (2.5-6 cm in diameter) localised to the region of the head of the pancreas were studied. All presented with obstructive jaundice which was relieved by biliary stenting prior to further treatment.

METHODS

Patients were photosensitised with 0.15 mg/kg meso-tetrahydroxyphenyl chlorin intravenously. Three days later, light was delivered to the cancer percutaneously using fibres positioned under computerised tomographic guidance. Three had subsequent chemotherapy.

RESULTS

All patients had substantial tumour necrosis on scans after treatment. Fourteen of 16 left hospital within 10 days. Eleven had a Karnofsky performance status of 100 prior to treatment. In 10 it returned to 100 at one month. Two patients with tumour involving the gastroduodenal artery had significant gastrointestinal bleeds (controlled without surgery). Three patients developed duodenal obstruction during follow up that may have been related to treatment. There was no treatment related mortality. The median survival time after photodynamic therapy was 9.5 months (range 4-30). Seven of 16 patients (44%) were alive one year after photodynamic therapy.

CONCLUSIONS

Photodynamic therapy can produce necrosis in pancreatic cancers with an acceptable morbidity although care is required for tumours invading the duodenal wall or involving the gastroduodenal artery. Further studies are indicated to assess its influence on the course of the disease, alone or in combination with chemoradiation.

Localization of experimental submucosal esophageal tumor in rabbits by using mono-L-aspartyl chlorin e6 and long-wavelength photodynamic excitation

BACKGROUND AND OBJECTIVE

To increase the applicability of photodynamic diagnosis with regard to deep-seated tumor, we illuminated tumors with a long-wavelength laser beam after photosensitization with mono-L-aspartyl chlorin e6 (NPe6).

STUDY DESIGN/MATERIALS AND METHODS

Rabbits with VX2 esophageal tumors were divided into four groups. The control group was not treated, and the other three groups were injected with 1, 2.5, and 5 mg/kg mono-L-aspartyl chlorin e6 (NPe6), respectively. After excitation with a 664-nm laser beam (10 mW, 10 seconds), the fluorescence image and the relative fluorescence intensity (tumor/normal tissue) were recorded every 2 hours up to 8 hours by a newly developed diode laser endoscopic fluorescence imaging system. The tissue concentration of NPe6 was examined by high performance liquid chromatography at 2, 4, and 6 hours after injection with 1 and 5 mg/kg NPe6.

RESULTS

The diode laser endoscopic fluorescence imaging system was able to selectively detect fluorescence from submucosal tumor by comparison with the surrounding normal mucosa after NPe6 injection. The fluorescence intensity correlated with NPe6 dose, selectively accumulated in the tumor tissue and relative intensity peaked at 6 hours after injection. No fluorescent images were detected in controls.

CONCLUSION

Given intravenously, NPe6 at a dose of 5 mg/kg and excited with a 664-nm wavelength laser beam 6 hours later can define experimentally induced deep-seated esophageal carcinoma in rabbits, by using an endoscopic fluorescence imaging system.

Foscan-mediated photodynamic therapy for a peritoneal-cancer model: drug distribution and efficacy studies

Distribution of the photosensitizer Foscan (meta-tetrahydroxyphenylchlorin, mTHPC), after i.v. or i.p. injection, was investigated in Wag/Rij rats bearing i.p. tumours. These results were compared with the efficacy of mTHPC-mediated photodynamic therapy for illumination intervals of 4 hr to 3 days. For the distribution experiments a single tumour (CC53I colon carcinoma) was implanted intra-abdominally in a fat pad, or a cell suspension (1 x 10(6) CC531 cells) was injected into the peritoneal cavity, which results in a dissemination of tumour nodules on the peritoneum. 14C-mTHPC was not selectively taken up in the single-tumour model after i.v. or i.p. injection, but higher concentrations were achieved for i.p. administration. For this tumour model the concentration ratios between tumour and normal tissue never exceeded a value of 3. In the disseminated-tumour model, an uptake of up to 40% of the injected dose was found per gram tumour at 4 hr after an i.p. injection and this resulted in very high (> 14) concentration ratios of tumour to normal tissues. Low uptake was found after the i.v. injection route (1% of the injected dose per gram tumour) with lower tumour/normal tissue ratios (<8). The efficacy of i.p. photodynamic therapy (IPPDT) was evaluated using the single-tumour model only. The lower abdomen was illuminated at 4 hr to 3 days after mTHPC, and tumour size was repeatedly measured via a small laparoscopy. Significant delay in tumour regrowth was achieved for 6 J x cm-2 at 1 day after i.v., or at 4 hr after i.p. mTHPC (p values 0.019 and 0.045 respectively). Response to PDT, of tumours implanted in the fat pad, was not greater for i.p. administration of the photosensitizer and there was a poor correlation between times of maximum drug uptake in tumours and optimal illumination times for PDT efficacy.

Intraperitoneal photodynamic therapy: comparison of red and green light distribution and toxicity

The aim of this study was to compare red (652 nm) and green (514 nm) light for photodynamic therapy (PDT) of the peritoneal cavity with emphasis on light distribution and toxicity. Red-light PDT was limited by intestinal toxicity and it was hypothesized that less penetrating green light would allow higher light doses to be used in the peritoneal cavity. Female non-tumor-bearing rats were photosensitized with mTHPC (meta-tetrahydroxyphenylchlorin, Foscan) intravenously or intraperitoneally and the peritoneum was illuminated using a minimally invasive technique. For both red and green light, the time of illumination was varied to give the required dose. Light fluence rate was measured in situ at multiple sites within the abdominal cavity. The toxicity experiments were carried out with a total of 160 J incident red or 640 J incident green light and a drug dose of 0.15 mg/kg Foscan. For red light a mean fluence rate of 55.2 +/- 38.5 mW cm-2 was measured, with a peak fluence rate of 128 mW cm-2 on the intestines. For green light the mean and peak fluence rates were 8.2 +/- 9.0 (i.e. including zero fluence rate measurements) and 28 mW cm-2, respectively. Intestines were most vulnerable to red light illumination. The intravenous injection route resulted in increased toxicity for red light, but for green light there were no major differences between intravenous and intraperitoneal routes. The 4 h interval between drug and illumination resulted in very little toxicity for both wavelengths. We conclude that for intraperitoneal PDT green light allows higher light doses than red light, but the light distribution over the peritoneum is much less favorable and may not be suitable for whole peritoneal illumination using a minimal-access technique.

In vivo laser-induced fluorescence imaging of a rat pancreatic cancer with pheophorbide-a

Laser-induced fluorescence (LIF) of pheophorbide-a (Ph-a) was used for imaging of a rat pancreatic tumor. Using a dimensionless function (the ratio of Ph-a fluorescence by bluish autofluorescence), the fluorescence contrasts between excised tumors and their paired pancreas were investigated up to 48 h after a 9 mg kg-1 Ph-a intravenous administration. Among five tested excitation wavelengths, 355 and 610 nm excitations gave the best distinctive contrasts, both 48 h after dye injection. The LIF imaging of six intrapancreatic tumors and six healthy pancreas was carried out in vivo using two laser excitations: 355 nm (Nd:YAG + tripling) for bluish autofluorescence and 610 nm (rhodamine 6G dye) for reddish autofluorescence and dye emission. Images were recorded through bandpass filters at 470 and 640 nm (autofluorescence) and at 680 nm (dye + autofluorescence) with an intensified charged-coupled device camera. Autofluorescence as Ph-a fluorescence images did not allow accurate LIF diagnosis of pancreatic carcinoma. An image processing, including for each pixel a computed division of Ph-a fluorescence (after subtraction of reddish autofluorescence) by bluish autofluorescence intensity generated poorly contrasted tumor images in five of six and false tumor localization in one of three of the tumor-bearing pancreas. A fitting of the digital 640 nm autofluorescence up to the mean 680 nm fluorescence intensity in pancreas prior to subtraction allowed a safe diagnosis to be made with well-contrasted tumor images. To assess automation ability of the processing, a same fitting coefficient (mean of individual values) was applied. In this way, false-negative (one of six) and false-positive (two of six) images were present in tumor-bearing animals as false-positive in one-half of the controls. A successful standardized procedure was then applied with a normalization of 640 and 680 nm pancreas intensities to a same set threshold prior processing. In opposition to thin-layered hollow organs, such as bronchial tube or digestive tract, LIF imaging of carcinoma inserted in a compact organ is exhausting. The use of a dye excitable in the red wavelength range (610 nm for Ph-a) may partly solve this problem, rendering LIF imaging more accurate and potentially automated.

Photodynamic therapy of a transplanted pancreatic cancer model using meta-tetrahydroxyphenylchlorin (mTHPC)

Pancreatic cancer is difficult to treat, even for tumours localized to the pancreas. Photodynamic therapy (PDT) is a non-thermal technique for producing localized tissue necrosis with light after prior administration of a photosensitizing drug and it could have a role in the local treatment of these cancers. We studied PDT in a transplanted cancer in the hamster pancreas using the photosensitizer mTHPC (meta-tetrahydroxyphenylchlorin). Fluorescence microscopy showed maximum levels of mTHPC in normal pancreas 2-4 days after sensitization and in tumour at 4-5 days. For PDT, animals were given 0.1 or 0.3 mg kg(-1) mTHPC and the tumour was treated at laparotomy 2 or 4 days later with red light (50 J at 650 nm, continuous or fractionated) delivered via a single fibre touching the tumour surface. The maximum zone of tumour necrosis (seen 3 days after PDT) was 8.7 mm in diameter with continuous irradiation, increasing to 12.4 mm with light fractionation (four equal fractions with 3 min between fractions). The main complication was sealed duodenal perforation, seen in 3 of 16 animals, probably due to inadequate shielding of the duodenum from the light. The duodenal problems seen in hamsters are unlikely to cause trouble in the much thicker human duodenum. PDT tumour necrosis in this animal model has now been shown with a range of photosensitizers, but mTHPC is attractive as it is likely to produce the largest volumes of necrosis around each treatment point with short light exposure times. This technique could have a role in the treatment of localized cancers of the pancreas in patients unsuitable for surgery and can now be considered for preliminary clinical trials.

Dynamic fluorescence changes during photodynamic therapy in vivo and in vitro of hydrophilic A1(III) phthalocyanine tetrasulphonate and lipophilic Zn(II) phthalocyanine administered in liposomes

The fluorescence emission of hydrophilic tetrasulphonated aluminium phthalocyanine (AlPcS4) and hydrophobic zinc phthalocyanine (ZnPc), bound to the membrane of liposomes, was investigated in vivo in an appropriate tumour model of the rat bladder and in RR 1022 epithelial cells of the rat. The sensitizers were administered systemically to the rats and photodynamic therapy (PDT) was performed 24 h later. During PDT treatment, the fluorescence was measured every 30 s. The fluorescence was excited with 633 nm light from an HeNe laser and the fluorescence spectra were detected with an optical multichannel analyser system. PDT was performed for both sensitizers using 672 nm light from an Ar+ dye laser. The fluorescence changes during PDT were significantly different for the two phthalocyanines. For AlPcS4, an initial fluorescence intensity increase, followed by subsequent photobleaching, was observed. In contrast, ZnPc fluorescence showed an exponential decrease and no increase at the start of treatment. Tumour necrosis 24 h after PDT was significant only for ZnPc. RR 1022 cells incubated for 24 h with AlPcS4 revealed a granular fluorescence pattern, whereas ZnPc was localized diffusely in the cytoplasm of the cells. In agreement with the in vivo measurements, subcellular relocalization and a fluorescence intensity increase were detected exclusively in the case of AlPcS4. Morphological changes at this time were significant only for ZnPc. The subcellular localization and fluorescence kinetics were obtained using a confocal laser scanning microscope.

Photodynamic therapy on the normal rabbit larynx with phthalocyanine and 5-aminolaevulinic acid induced protoporphyrin IX photosensitisation

Photodynamic therapy (PDT) is a promising technique for the treatment of small tumours in organs where it is essential to minimise damage to immediately adjacent normal tissue as PDT damage to many tissues heals by regeneration rather than scarring. As preservation of function is one of the main aims of treating laryngeal tumours, this project studied the effects of PDT on the normal rabbit larynx with two photosensitisers, endogenous protoporphyrin IX (PPIX) induced by the administration of 5-aminolaevulinic acid (ALA) and disulphonated aluminium phthalocyanine (AIS2Pc). The main aims of the study were to examine the distribution of protoporphyrin IX and AIS2Pc by fluorescence microscopy in the different regions of the larnyx and to assess the nature and subsequent healing of PDT damage. Peak levels of PPIX were found 0.5-4 h after administration of ALA (depending on dose) with highest levels in the epithelium of the mucosa. With 100 mg kg-1, PDT necrosis was limited to the mucosa, whereas with 200 mg kg-1 necrosis extended to the muscle. With 1 mg kg-1 AIS2Pc, 1 h after administration, the drug was mainly in the submucosa and muscle, whereas after 24 h, it was predominantly in the mucosa. PDT at 1 h caused deep necrosis whereas at 24 h it was limited to the mucosa. All mucosal necrosis healed by regeneration whereas deeper effects left some fibrosis. No damage to cartilage was seen in any of the animals studied. The results of this study have shown that both photosensitisers are suitable for treating mucosal lesions of the larynx, but that for both it is important to optimise the drug dose and time interval between drug and light to avoid unacceptable changes in normal areas.

Distribution and photodynamic effects of meso-tetrahydroxyphenylchlorin (mTHPC) in the pancreas and adjacent tissues in the Syrian golden hamster

Photodynamic therapy (PDT) has the potential to destroy small tumours with safe healing of adjacent normal tissue. This study looks at the effects of PDT on the normal pancreas and adjacent tissues in hamsters using the photosensitiser meso-tetrahydroxyphenylchlorin (mTHPC). Pharmacokinetic studies used fluorescence microscopy on sections of pancreas, stomach and duodenum 1 h to 6 days after mTHPC. Highest levels of sensitiser were seen in the gastric and duodenal mucosa and in the acinar pancreas after 2-4 days. For PDT, light at 652 nm was delivered by placing a 0.2 mm diameter bare-ended fibre against the tissue. An energy of 50 J was used 2 or 4 days after 0.1 or 0.3 mg kg-1 mTHPC and animals killed 1 to 7 days later. Maximum necrosis was seen 3 days after PDT with lesions up to 4 mm in pancreas, 4.5 mm in duodenum and 2.5 mm in stomach. By fractionating the light dose, the lesion size could be increased by 30%. The main complication was free or sealed duodenal perforation (avoided by shielding the duodenum). Partial, reversible bile duct obstruction was seen occasionally. There was no macroscopic damage to the bile ducts or major blood vessels. Apart from the duodenum, all lesions healed safely. In this animal model, only the duodenum was at risk of serious, irreversible damage. Treatment is likely to be safer in the much thicker human duodenum. mTHPC is a powerful photosensitiser and suitable for further study for tumours in the region of the pancreas although care is required near the duodenum.

Photodynamic imaging of a rat pancreatic cancer with pheophorbide a

Laser-induced fluorescence of pheophorbide a (Ph-a) was used for in vitro photodynamic imaging (PDI) of a rat pancreatic acinar tumor. A 400 nm excitation induced a 470 nm autofluorescence and a 678 nm dye fluorescence in tumors and their surrounding pancreas 24 h after a 9 mg kg-1 body weight Ph-a intravenous administration. With lower intensities in these blood-rich tumors than in pancreas, Ph-a fluorescence signals are unable to provide tumor images. A dimensionless function (the ratio of Ph-a fluorescence by autofluorescence, called Rt for the tumor and Rp for the pancreas) was used for fluorescence contrast calculation (C = Rt/Rp) between six tumors and their paired pancreas. Among five available laser excitation wave-lengths, only the 355 nm excitation gave a distinctive contrast (C = 1.5). The PDI of six intrapancreatic tumors and their intraperitoneal metastasis and of two control normal pancreas was thus performed ex vivo using a 355 nm excitation source delivered by a tripled Nd:YAG laser and a charged-coupled device camera. Fluorescence images were recorded at 680 nm (dye), 640 nm (background) and 470 nm (autofluorescence) through three corresponding 10 nm width bandpass filters. Computed division for each pixel of Ph-a fluorescence values by autofluorescence generated false color image. In this way, contrasted tumor images were obtained. But in five out of six animals false-positive images were present due to an autofluorescence decrease in some normal pancreatic areas. A 470 nm autofluorescence imaging on the same tumors gave in all cases false-positive image and false-negative in half of the cases. These observations suggest that autofluorescence alone is unable to achieve accurate PDI of pancreatic carcinoma and that using Ph-a as a PDI dye needs strong improvements.

Photodynamic therapy for malignant tumours of the ampulla of Vater

Ten patients with ampullary carcinoma, not suitable for surgery, were treated with endoscopic photodynamic therapy (PDT) to evaluate the feasibility and safety of treatment. Patients received 4 mg kg-1 of haematoporphyrin derivative intravenously. Two days later, a duodenoscopy was performed and red (630 nm) light delivered to the tumour at fixed energy densities of 50 J or 200 J cm-1 per application, depending on the type of optical fibre used. The tumours were treated by three or four light applications at each session. Treatment was repeated up to five times at intervals of three to six months. The sole complication of PDT was moderate skin photosensitivity, which occurred in three patients. Tumour size was assessed at four to eight weekly intervals. In the absence of macroscopic tumour, biopsy specimens were taken. In three patients with small tumours confined to the ampulla, remission was obtained for periods ranging from eight to 12 months. In a further four patients with small tumours bulk was greatly reduced. There was little response in three patients with extensive duodenal involvement. Therefore PDT for ampullary carcinoma is both feasible and safe, and with refinement may prove curative for small tumours.

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.

Experimental pancreatic cancer in the rat treated by photodynamic therapy

Selective histological necrosis of experimental pancreatic carcinoma by photodynamic therapy (PDT) has been successful with haematoporphyrin derivatives and phthalocyanine as photosensitizers. This report describes the feasibility of PDT with pheophorbide A as the photosensitizer to treat azaserine-induced pancreatic rat carcinoma and analyses survival of the animals. An organ distribution study 24 h after pheophorbide A administration (9 mg/kg intravenously) gave a selectivity ratio of 13.5:1 between tumour and surrounding tissue. Light of 660 nm and 100 J/cm2 induced selective necrosis of the tumour. Six of nine rats were cured in 120 days whereas all 36 control animals died within 35 days (P < 0.01). The pancrease and hepatic pedicle were relatively unaffected by PDT, but the duodenum was injured.

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 normal rat arteries after photosensitisation using disulphonated aluminium phthalocyanine and 5-aminolaevulinic acid

Photodynamic therapy of cancer exposes adjacent arteries to the risk of injury and the possibility of haemorrhage and thrombosis. The nature of photodynamic injury to normal arteries has not been satisfactorily defined, and the ability of arteries to recover with time is unclear. To clarify these issues, we have investigated the effects of PDT on rat femoral arteries, using a second-generation photosensitiser, disulphonated aluminium phthalocyanine, and a new method of photosensitisation, using endogenous synthesis of protoporphyrin IX following systemic administration of 5-aminolaevulinic acid (ALA). Pharmacokinetic studies of sensitiser fluorescence were carried out to determine peak levels of sensitiser. Subsequently photodynamic therapy at times corresponding to maximal fluorescence was performed using two light doses, 100 and 250 J cm-2. The nature of injury sustained and recovery over a 6 month period was investigated. Three days following PDT, all vessels treated showed complete loss of endothelium, with death of all medial smooth muscle cells, leaving an acellular flaccid artery wall. No vascular occlusion, haemorrhage or thrombosis was found. A striking feature was the lack of inflammatory response in the vessel wall at any time studied. Re-endothelialisation occurred in all vessels by 2 weeks. The phthalocyanine group showed repopulation of the media with smooth muscle cells to be almost complete by 3 months. However, the ALA group failed to redevelop a muscular wall and remained dilated at 6 months. Luminal cross-sectional area of the ALA-treated group was significantly greater than both control and phthalocyanine groups at 6 months. All vessels remained patent. This study indicates that arteries exposed to PDT are not at risk of catastrophic haemorrhage or occlusion, a finding that is of significance for both the local treatment of tumours and the use of PDT as an intraoperative adjunct to surgery for the ablation of microscopic residual malignant disease.

Time-resolved fluorescence spectroscopy and intracellular imaging of disulphonated aluminium phthalocyanine

Spectroscopic studies were carried out on the photosensitizer disulphonated aluminium phthalocyanine (AlS2Pc) which has prospective applications in photodynamic therapy. The fluorescence lifetimes of AlS2Pc were measured in a range of model systems and cultured leukaemic cells using laser excitation and time-correlated, single-photon-counting detection. In an investigation of non-covalent protein binding, we studied AlS2Pc in the presence of human serum albumin (HSA) in 0.1 M phosphate-buffered saline at pH 7.4. On addition of excess concentrations of HSA, small red shifts in the fluorescence and absorbance spectra were observed, together with an increase in fluorescence polarization anisotropy, consistent with binding of the phthalocyanine. Fluorescence decays could be resolved into two lifetimes for bound AlS2Pc with a dominant component of 5.5 ns and a minor component of 1 ns. Fluorescence imaging and time-resolved microfluorometry were carried out on intracellular AlS2Pc using leukaemic K562 cells. Microscopic imaging with a charge-coupled device (CCD) camera revealed that AlS2Pc fluorescence predominated in a discrete perinuclear region which was then probed selectively by a focused laser spot for fluorescence lifetime measurements. Bi-exponential decays with lifetime components of 6.1 and 2.2 ns were observed. On irradiation at 633 nm, the fluorescence intensity increased initially and subsequently declined due to photodegradation.

Biological activities of phthalocyanines--XVI. Tetrahydroxy- and tetraalkylhydroxy zinc phthalocyanines. Effect of alkyl chain length on in vitro and in vivo photodynamic activities

Zinc phthalocyanine substituted with four hydroxyl groups attached to the macrocycle, either directly or via spacer chains of three or six carbon atoms, were tested for their photodynamic ability to inactivate Chinese hamster lung fibroblasts (line V-79) in vitro, and to induce regression of EMT-6 tumours grown subcutaneously in Balb/c mice. Their potential to inflict direct cell killing during photodynamic therapy was investigated by examining vascular stasis immediately following photoirradiation using fluorescein as a marker, and also by an in vivo/in vitro EMT-6 cell survival assay. Both of the tetraalkylhydroxy substituted zinc phthalocyanines are effective photodynamic sensitisers in vivo with the tetrapropylhydroxy compound exhibiting about twice the activity of the tetrahexylhydroxy analogue. The differences in activities were accentuated in vitro, the tetrapropylhydroxy compound was two orders of magnitude more potent than the tetrahexylhydroxy analogue in photoinactivating V-79 cells. The tetrahydroxy compound lacking spacer chains failed to exhibit photodynamic activity in either system. Tumour response with the active compounds was preceded by vascular stasis immediate following irradiation which suggests, together with the absence of activity in the in vivo/in vitro assay, that tumour regression involves an indirect response to the photodynamic action rather than direct cell killing. These data demonstrate the importance of the spatial orientation of functional groups around the macrocycle of photosensitisers for their efficacy in the photodynamic therapy of cancer.

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.

Increasing the effect of photodynamic therapy on the RIF-1 murine sarcoma, using the bioreductive drugs RSU1069 and RB6145

The effect of combining photodynamic therapy (PDT) and bioreductive drugs has been investigated using the RIF-1 experimental murine tumour. Light was delivered interstially to the tumour at 675 nm using a single optical fibre attached to an argon-ion dye laser. The photosensitizer was disulphonated aluminium phthalocyanine (AlS2Pc) and the bioreductive drugs were the dual function nitroimidazole RSU1069 and its pro-drug RB6145. Varying the time between administration of the photosensitizer and light delivery (TL) from 30 min to 24 h had little influence on the extent of the anti-tumour effect of PDT alone, as measured by the regrowth delay endpoint. When the bioreductive drug was included in the treatment, administered 20 min before light irradiation, regrowth delay was greatly increased. The effectiveness of the combined treatment was optimum for short values of TL (about 1 h). Fluorescence microscopy was used to investigate the distribution of the photosensitizer within the tumours. This showed that the compound was mainly confined to the tumour vasculature over the first few hours post-treatment. The high efficacy of the combined treatment of PDT and bioreductive drugs for short values of TL suggest that photodynamic action, during the period when the photosensitizer AlS2Pc is confined to the vasculature, enhances the severity of tumour hypoxia which is sufficient to induce activation of the bioreductive drugs.