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.     

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

Necrosis of small volumes of tumour tissue with photodynamic therapy (PDT) can be achieved relatively easily. For this to be clinically relevant, it is essential to know what the same treatment parameters do to adjacent normal tissues into which the tumour has spread. For pancreatic cancers, local spread to vital structures is common. We have studied chemical extraction, microscopic fluorescence kinetics and photodynamic effects of disulphonated aluminum phthalocyanine (AlS2Pc) in normal pancreas and adjacent tissues in hamsters. Chemical extraction exhibited a peak duodenal concentration of AlS2Pc 48 h after sensitisation, with levels much higher than in stomach and pancreas. With microscopic fluorescence photometry highest levels were seen in duodenal submucosa and bile duct walls 48 h after photosensitisation. Pancreatic ducts, duodenal mucosa and gastric mucosa and submucosa exhibited intermediate fluorescence with relatively weak fluorescence in pancreatic acinar tissue and the muscle layer of the stomach. As expected, on the basis of fluorescence intensity and chemical extraction studies, the duodenal and bile duct wall were the most vulnerable tissues to photodynamic therapy. When the dose of 5 mumol kg-1 of sensitiser was used, duodenal perforations, gastric ulcers and transudation of bile from the bile duct occurred. However, the lesions in the stomach and bile duct healed without perforation or obstruction, so only the duodenum was at risk of serious, irreversible damage. Using a lower dose of photosensitiser markedly reduced damage.     

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.Int. J. Cancer 71: 937-942, 1997. © 1997 Wiley-Liss Inc.     

Photodynamic therapy using intravenous delta-aminolaevulinic acid-induced protoporphyrin IX sensitisation in experimental hepatic tumours in rats.

The efficacy of photodynamic therapy (PDT) using delta-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) sensitisation and laser light at 635 nm was investigated in the treatment of experimental hepatic tumours. The model of liver tumours was induced either by local inoculation or by administration of tumour cells through the portal vein in rats. ALA at a dose of 60 mg kg(-1) b.w. was intravenously administered 60 min before PDT. PpIX accumulation in tumour, normal liver and abdominal wall muscle was detected by means of laser-induced fluorescence (LIF). Laser Doppler imaging (LDI) was used to determine changes in the superficial blood flow in connection with PDT. Histopathological examinations were performed to evaluate the PDT effects on the tumour and the surrounding liver tissue, including pathological features in the microvascular system. The accumulation of PpIX, as monitored by LIF, showed high fluorescence intensities at about 635 nm in both the hepatic tumour tissue and normal liver and low values in the abdominal wall. LDI demonstrated that the blood flow in the treated tumour and its surrounding normal liver tissue decreased immediately after the PDT, indicating an effect on the vascular system. A large number of thrombi in the irradiated tumour were found microscopically 3 h after the PDT. The tumour growth rate showed a marked decrease when evaluated 3 and 6 days after the treatment. These results show that the ALA-PDT is effective in the inhibition of growth of experimental hepatic tumours.     

ALA光动力诊断导向显微手术与光动力治疗兔脑VX2转移瘤的比较研究

背景与目的：光动力治疗脑胶质瘤是新的疗法之一。实验比较研究光敏剂ALA（5-氨基乙酰丙酸）在光动力诊断（photodynamic diagnosis,PDD）导向显微手术和（或）光动力治疗（photodynamic therapy,PDT）兔脑VX2转移瘤的疗效。方法：50只新西兰大白兔脑内植入VX2瘤块形成移植瘤模型后,随机分为对照组（不治疗）、普通光源显微手术组、单次PDT组、PDD导向显微手术组及PDD导向显微手术辅以PDT组。重点观察比较各组荷瘤动物平均生存期。结果：平均生存期分别为对照组25.20±2.53天、普通光源显微手术组51.40±3.63天、单次PDT组47.40±2.63天、PDD导向显微手术组56.40±3.31天、PDD导向显微手术辅以PDT组58.90±3.28天;与对照组相比,各治疗组的生存期明显延长,以PDD导向显微手术辅以PDT治疗最为显著。结论：单次ALA-PDT可明显延长荷瘤动物生存期;PDD导向显微手术组较普通光源显微手术组显著延长动物生存期;ALA可用于VX2鳞癌脑转移瘤的PDD导向显微手术而且还可用于PDT,ALA-PDD＋PDT可能更有效地治疗VX2脑转移瘤。     

Photodynamic therapy of a mouse glioma: intracranial tumours are resistant while subcutaneous tumours are sensitive

Subcutaneous and intracranial VMDk tumours were treated with photodynamic therapy (PDT) using a new sensitiser, m-THPP. Subcutaneous tumours were highly sensitive to PDT but intracranial tumours were much more resistant, requiring a 30-fold increase in sensitiser dose to produce equivalent levels of necrosis. Resistance of intracerebral tumours was not due to failure of the sensitiser to enter tumours. Necrosis of intracranial tumours was increased when mice breathed 100% oxygen during PDT while subcutaneous tumour necrosis was unaffected.     

Timing of illumination is essential for effective and safe photodynamic therapy: a study in the normal rat oesophagus

5-Aminolaevulinic acid (ALA)-induced, protoporphyrin IX (PpIX)-mediated photodynamic therapy (PDT) is an experimental treatment modality for (pre)malignant oesophageal lesions. This study aimed to optimize the time of illumination after ALA administration. Six groups of eight rats received 200 mg kg(-1) ALA orally, eight rats served as controls. Illumination was performed at 1, 2, 3, 4, 6 or 12 h after ALA administration with a 1-cm cylindrical diffuser placed in a balloon catheter (laser parameters: 633 nm, 25 J radiant energy, power output 100 mW). During illumination, fluorescence measurements and light dosimetry were performed. Animals were sacrificed at 48 h (n = 4) or 28 days (n = 4) after PDT. At day 28, an oesophagogram was performed. Largest PpIX fluorescence was found at 3 h after ALA administration. In vivo fluence rate was three times higher than the calculated incident fluence rate. At 48 h after PDT, major epithelial damage was found in all animals illuminated at 2 h, whereas less epithelial damage was found at 3-6 h and none at 1 and 12 h. In animals illuminated at 4, 6 and 12 h, but not at 2 h, oesophagograms showed severe dilatations and histology showed loss of Schwann cells. These results demonstrate that the choice of time interval between ALA administration and illumination is critical for achieving epithelial damage without oesophageal functional impairment. A short interval of 2-3 h seems to be most appropriate.     

Selective accumulation of ALA-induced PpIX and photodynamic effect in chemically induced hepatocellular carcinoma

The possibility of 5-aminolaevulinic acid-based photodynamic therapy (ALA-PDT) for liver cancer was investigated using a chemically induced hepatocellular carcinoma (HCC) model. Endogenously synthesised protoporphyrin IX (PpIX) following the administration of ALA is an effective photosensitiser for PDT. We determined the fluorescence intensity of PpIX in HCC and nontumoral tissue in the liver. 5-Aminolaevulinic acid was intravenously injected to male Fisher rats with HCC at a dose of 500 mg x kg(-1), and the fluorescence intensity in each tissue sample excised from liver was measured with a spectrofluorometer at 1, 3 and 6 h after administration. Fluorescence intensity was at a peak of 3 h after administration in both HCC and nontumoral tissue. The accumulation of PpIX in HCC was higher than that in the nontumoral tissue at 1 h (P<0.001) and 3 h (P<0.05) after ALA administration. Based on these results, PDT was performed on HCC at 3 h after 500 mg x kg(-1) ALA administration before laser irradiation of 30 J per tumour. Antitumour effect was more evident in HCC than in the nontumoral tissue surrounding HCC. These findings suggest the possibility to detect HCC by fluorescence and to treat HCC by light.     

In vivo fluorescence kinetics and photodynamic therapy using 5-aminolaevulinic acid-induced porphyrin: increased damage after multiple irradiations.

The kinetics of fluorescence in tumour (TT) and subcutaneous tissue (ST) and the vascular effects of photodynamic therapy (PDT) were studied using protoporphyrin IX (PpIX), endogenously generated after i.v. administration of 100 and 200 mg kg-1 5-aminolaevulinic acid (ALA). The experimental model was a rat skinfold observation chamber containing a thin layer of ST in which a small syngeneic mammary tumour grows in a sheet-like fashion. Maximum TT and ST fluorescence following 200 mg kg-1 ALA was twice the value after 100 mg kg-1 ALA, but the initial increase with time was the same for the two doses in both TT and ST. The fluorescence increase in ST was slower and the maximum fluorescence was less and appeared later than in TT. Photodynamic therapy was applied using green argon laser light (514.5 nm, 100 J cm-2). Three groups received a single light treatment at different intervals after administration of 100 or 200 mg kg-1 ALA. In these groups no correlation was found between the fluorescence intensities and the vascular damage following PDT. A fourth group was treated twice and before the second light treatment some fluorescence had reappeared after photobleaching due to the first treatment. Only with the double light treatment was lasting TT necrosis achieved, and for the first time with any photosensitiser in this model this was accomplished without complete ST necrosis.     

The monitoring of the accumulation of protoporphyrin IX in Walker tumours by subcutaneous administration of delta-aminolevulinic acid

Photodynamic therapy with protoporphyrin IX induced by delta-aminolevulinic acid (ALA) is mainly applied for the treatment of human superficial skin cancer. In this paper we present our study on photodynamic therapy (PDT) of the implanted Walker tumours using subcutaneous administration of ALA to improve the availability of ALA in the skin. We determined the accumulation and localization of protoporphyrin IX (PpIX) after subcutaneous administration of different concentrations of ALA in a physiological saline solutions, using fluorescence imaging technique. The results obtained indicate that PpIX accumulation depends on the concentration of ALA. The temporal behavior of PpIX fluorescence has shown a clear demarcation of tumoural zone depending on the post-administration time and the administrated concentration of the ALA solution. Further studies are needed to confirm these encouraging results and to define the PDT protocols using subcutaneous administration of ALA solution     

Photobleaching during and re-appearance after photodynamic therapy of topical ALA-induced fluorescence in UVB-treated mouse skin

Photodynamic therapy (PDT) using protoporphyrin IX (PpIX) induced by topically applied 5-aminolevulinic acid (ALA) seems a promising alternative for the treatment of superficial non-melanoma skin cancer and actinic keratosis. In this study, the kinetics of new PpIX fluorescence arising after a PDT treatment that had photobleached the original fluorescence were determined. Our purpose was to examine the feasibility of multiple irradiations, following a single topical ALA application, to increase PDT efficacy. In addition, photobleaching during PDT and the fluorescence spectra during and after PDT were studied. As a model we used hairless mice with and without UVB-induced skin lesions. ALA was applied to the skin for 4 hr. An illumination was delivered either immediately after application or 6 hr after the end of the application (at interval of maximum fluorescence). During PDT, the fluorescence of normal skin decreased at a faster rate than the fluorescence of the skin lesions. In the fluorescence study after PDT, the areas treated immediately post-application showed a fluorescence increase over time similar to that in non-treated areas on the same mice. A remarkable result was that the fluorescence of areas treated at maximum fluorescence increased, whereas the fluorescence of non-treated areas did not increase over time. With both treatment intervals the new fluorescence showed a characteristic PpIX spectrum. Our results demonstrate that a second illumination, when new PpIX fluorescence has been formed, may increase PDT efficacy after topical ALA application. This finding has been demonstrated previously for systemic ALA administration. Int. J. Cancer 72:110–118, 1997. © 1997 Wiley-Liss Inc.     

Photodynamic therapy with porphyrin and phthalocyanine sensitisation: quantitative studies in normal rat liver

Selective sensitisation of malignant tumours to monochromatic light (photodynamic therapy, PDT) is a promising approach to cancer treatment, but current sensitisers are unsatisfactory and the parameters controlling effects produced in normal and neoplastic tissue are poorly understood. To quantify the effects in a relatively homogeneous organ, we carried out experiments in the livers of normal rats following systemic sensitisation with haematoporphyrin derivative (HpD) and a new sensitiser, a sulphonated aluminium phthalocyanine (AlSPc) using light from an Argon pumped tunable dye laser. Damage from PDT (dominant at 100 mW laser power) could be distinguished from that due to local hyperthermia (dominant at 400 mW). For both sensitisers, the extent of PDT necrosis increased with the applied light energy and was abolished by occluding the hepatic blood flow during therapy. With HpD, the extent of PDT necrosis was maximum with only a few hours between sensitisation and therapy, and was not detectable when this interval was increased to a week. With AlSPc, the extent of necrosis in liver changed little with sensitisation times from 1 h to 1000 h (6 weeks), and declined slowly thereafter, matching the amount of AlSPc measurable by alkali extraction, although prolonged photosensitisation was not seen with AlSPc in muscle. Less cutaneous photosensitivity was seen with AlSPc than with HpD. AlSPc is easier to produce and handle than HpD, has a more appropriate strong absorption peak (at 675 nm) and from these results, warrants further study as a photosensitiser for PDT.     

Topical and intratumoral photodynamic therapy with 5-aminolevulinic acid in a subcutaneous murine mammary adenocarcinoma.

One of the most promising substances used in photodynamic therapy (PDT) is 5-aminolevulinic acid (ALA), which induces endogenous synthesis and accumulation of porphyrins in malignant cells. In this paper we have shown that both topical and intratumoral administration of ALA in a subcutaneously implanted mammary carcinoma produced a significant synthesis of porphyrins and subsequent sensitization to laser light. Porphyrin accumulation was greater when ALA was administered intratumorally and tumour/normal skin porphyrin concentration ratios were higher compared with topical application. Irradiation was optimal between 2 and 3 h after topical application of 50 mg of a 20% ALA cream and 2-4 h after intratumoral administration of 30 mg ALA/cm3. The pattern of tumour response evaluated as the delay of tumour growth was similar following either route of drug administration. Applications of PDT were performed once, twice or three times in the study. The response to successive applications was constant for the same tumour, indicating that no resistance was acquired. Microscopic analysis showed both induction of foci of necrosis and haemorrhage, morphological features of apoptotic cells and total absence of cellular immune response. This paper reports on PDT with topical ALA in a subcutaneous carcinoma leading to tumour growth delay. These findings may have great relevance in the treatment of cutaneous metastasis of mammary carcinomas.     

Enhancement of 5-aminolaevulinic acid-induced photodynamic therapy in normal rat colon using hydroxypyridinone iron-chelating agents.

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(-1)). This study investigates whether hydroxypyridinone iron-chelating agents can be used to enhance the tissue levels of PPIX, without increasing the administered dose of ALA. Quantitative charge-coupled device (CCD) fluorescence microscopy was employed to study PPIX fluorescence pharmacokinetics in the colon of normal Wistar rats. The iron chelator, CP94, when administered with ALA was found to produce double the PPIX fluorescence in the colonic mucosa, compared with the same dose of ALA given alone and to be more effective than the other iron chelator studied, CP20. Microspectrofluorimetric studies demonstrated that PPIX was the predominant porphyrin species present. PDT studies conducted on the colonic mucosa showed that the simultaneous administration of 100 mg kg(-1) CP94 i.v. and 50 mg kg(-1) ALA i.v. produced an area of necrosis three times larger than similar parameters without the iron-chelating agent with the same light dose. It is possible, therefore, to increase the amount of necrosis produced by ALA-induced PDT substantially, without increasing the administered dose of ALA, through the simultaneous administration of the iron-chelating agent, CP94.     

光动力对人子宫颈癌Hela细胞的杀伤作用及光动力剂量的研究

目的 观察氨基酮戊酸(5-Aminolevulinic acid,ALA)介导的光动力疗法(photodynamic therapy,PDT)对人子宫颈癌Hela细胞株的杀伤效应,探讨最佳光动力剂量.方法 实验分为空白对照组、单纯激光组、单纯光敏剂组和实验组(照光+光敏剂).对体外培养的人子宫颈癌Hela细胞株进行光动力实验,应用MTT法检测其光密度值(OD570),观察不同光动力剂量下对人子宫颈癌Hela细胞在体外的抑制作用,并绘制其抑制曲线和观察其形态学变化.结果 实验组于治疗后明显抑制体外培养的人子宫颈癌Hela细胞,而空白对照组、单纯使用光敏剂组及单纯激光照射组对细胞增殖均无明显影响.光动力治疗后12 h,镜下细胞变形,细胞内出现大量的核碎裂、核融解、核消失等坏死征象,少部分表现为凋亡.结论 ALA介导的光动力疗法(ALA-PDT)可明显抑制体外培养的人子宫颈癌Hela细胞株的生长,ALA浓度为 0.5 mmol/L、激光剂量为5J/cm2是杀伤Hela 细胞的最佳剂量.     

The detection of phthalocyanine fluorescence in normal rat bladder wall using sensitive digital imaging microscopy

The ability to detect photosensitisers in tissue at a microscopical level is important when studying photodynamic therapy (PDT) in both normal and malignant tissue. We have studied the fluorescence distribution of aluminium sulphonated phthalocyanine (A1SPc) in the normal rat bladder using a cooled CCD (charge coupled device) imaging system with computerised image processing. This system makes it possible to carry out a quantitative assessment of photosensitiser fluorescence in the various layers of the bladder wall. The highest fluorescence intensities were obtained within 1 h of intravenous administration but there was little selectivity of uptake between layers. A1SPc was eliminated from the deeper muscle layers more quickly than from the superficial layers of the bladder wall so that by 24 h a 4:1 ratio of fluorescence intensity was apparent which persisted at least until 72 h, although the absolute amount of photosensitiser declined. Following irradiation by red light (675 nm), photobleaching of the sensitiser in the deeper layers further increased this ratio. Direct absorption of A1SPc by the bladder wall following intravesical administration proved unreliable.     

Photodynamic therapy of tumours with hexadecafluoro zinc phthalocyanine formulated in PEG-coated poly(lactic acid) nanoparticles

Hexadecafluoro zinc phthalocyanine (ZnPcF₁₆), a second-generation sensitizer for the photodynamic therapy (PDT) of cancer, was formulated in polyethylene-glycol-coated poly(lactic acid) nanoparticles (PEG-coated PLA-NP) and tested in EMT-6 tumour-bearing mice for its photodynamic activity. The tumour response was compared to that induced by the same dye formulated as a Cremophor EL (CRM) emulsion. Formulation in the biodegradable NP improved PDT response of the tumour while providing prolonged tumour sensitivity towards PDT. © 1996 Wiley-Liss, Inc.     

Oral versus intravenous administration of 5-aminolaevulinic acid for photodynamic therapy.

Endogenously synthesised protoporphyrin IX (PpIX) following the administration of 5-amino-laevulinic acid (ALA) is an effective photosensitiser for photodynamic therapy (PDT). Following intravenous administration, PpIX accumulates predominantly in mucosa of hollow viscera and on light exposure, mucosal ablation results with relative sparing of the submucosa and muscularis layers. Oral administration is effective with ALA in contrast to conventional exogenous photosensitisers such as haematoporphyrin derivative and phthalocyanines. Oral administration of ALA is also simpler, safer, cheaper and more acceptable to patients. We studied the porphyrin sensitisation kinetics profile in the stomach, colon and bladder in normal rats following enterally and parenterally administered ALA using microscopic fluorescence photometric studies of frozen tissue sections. Mucosal cells in all three organs exhibit higher fluorescence levels as compared with underlying smooth muscle following both intravenous and oral administration. Peak concentration were seen 4 h after sensitisation at the highest doses used (200 mg kg-1 i.v., 400 mg kg-1 oral), and slightly earlier with lower doses. The temporal kinetics of both routes of administration were similar although a higher oral dose was required to achieve the same tissue concentration of PpIX. The highest level of fluorescence was achieved in the gastric mucosa and in decreasing levels, colonic and bladder mucosa. A similar degree of mucosal selectivity was achieved in each organ with each route of administration but an oral dose in excess of 40 mg kg-1 was required to achieve measurable PpIX sensitisation. In a pilot clinical study, two patients with inoperable rectal adenocarcinomas were given 30 mg kg-1 and one patient with sigmoid colon carcinoma was given 60 mg kg-1 ALA orally. Serial biopsies of normal and tumour areas were taken over the subsequent 24 h. Fluorescence microscopy of these specimens showed maximum accumulation of PpIX 4 to 6 h after administration of 30 mg kg-1 ALA. There was greater PpIX accumulation in tumour than adjacent normal mucosa in two patients. Preferential PpIX accumulation in tumour was greater in the patient receiving 60 mg kg-1 ALA.     

A comparative study of tissue distribution and photodynamic therapy selectivity of chlorin e6, Photofrin II and ALA-induced protoporphyrin IX in a colon carcinoma model.

An in vivo study of tissue distribution kinetics and photodynamic therapy (PDT) using 5-aminolaevulinic acid (ALA), chlorin e6 (Chl) and Photofrin (PII) was performed to evaluate the selectivity of porphyrin accumulation and tissue damage effects in a tumour model compared with normal tissue. C26 colon carcinoma of mice transplanted to the foot was used as a model for selectivity assessment. Fluorescence measurements of porphyrin accumulation in the foot bearing the tumour and in the normal foot were performed by the laser-induced fluorescence (LIF) system. A new high-intensity pulsed light delivery system (HIPLS) was used for simultaneous irradiation of both feet by light in the range of 600-800 nm, with light doses from 120 to 300 J cm-2 (0.6 J cm-2 per pulse, 1 Hz). Photoirradiation was carried out 1 h after injection of ALA, 3 h after injection of Chl and 24 h after injection of PII. A ratio of porphyrin accumulation in tumour vs normal tissue was used as an index of accumulation selectivity for each agent. PDT selectivity was determined from the regression analysis of normal and tumour tissue responses to PDT as a function of the applied light dose. A normal tissue damage index was defined at various values (50, 80 and 100%) of antitumour effect. The results of the LIF measurements revealed different patterns of fluorescence intensity in tumour and normal tissues for ALA-induced protoporphyrin IX (ALA-PpIX), Chl and PII. The results of PDT demonstrated the differences in both anti-tumour efficiency and normal tissue damage for the agents used. The selectivity of porphyrin accumulation in the tumour at the time of photoirradiation, as obtained by the LIF measurements, was in the order ALA-PpIX > Chl > PII. PDT selectivity at an equal value of anti-tumour effect was in the order Chl > ALA-PpIX > PII. Histological examination revealed certain differences in structural changes of normal skin after PDT with the agents tested. The results of PDT selectivity assessment with respect to differences in mechanisms of action for ALA, Chl and PII are discussed.     

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.