Porphyrin photosensitization and phototherapy

Pharmacokinetic studies with zinc(II)-phthalocyanine in tumour-bearing mice

Zn(II)-phthalocyanine (Zn-Pc) incorporated into unilamellar liposomes of dipalmitoylphosphatidylcholine has been injected intraperitoneally (0.5 mg kg-1) to BALB/c mice bearing a transplanted MS-2 fibrosarcoma. The drug is specifically transported by serum lipoproteins and cleared from the serum via the bile-gut pathway in a biphasic process: approximately 60% of Zn-Pc is eliminated with a serum half-life of approximately 9 hours, while the remaining aliquot is eliminated at a very slow rate. Several normal tissues take up the drug within 3 hours after administration but release it almost completely after 24-48 hours. On the other hand, the tumour shows a maximum concentration of Zn-Pc (approximately 0.6 microgram g-1 of tissue) after 18-24 hours; at this time, the ratio between the Zn-Pc levels in the tumour and the muscle (which represents the surrounding normal tissue) is approximately 7.5. The results are discussed in terms of a possible use of Zn-Pc as a photosensitizer in the photodynamic therapy of tumours.

THE DEGRADATION OF CHLOROPHYLL - A BIOLOGICAL ENIGMA

Some 10⁹ tonnes of chlorophyll are destroyed each year on land and in the oceans. The fate of these chlorophylls is, however, largely unknown. This review describes the developmental stages at which chlorophyll breakdown occurs in aquatic and terrestrial biological systems, and the destruction arising from herbivory, disease, pollution and other physical hazards. At the cellular level, an attempt is made to separate the breakdown of chlorophyll during senescence from the many other events associated with cell destruction and death. A consideration of the more important chemical and biophysical properties of chlorophylls and their derivatives is provided, together with data on their spectral properties. The biosynthetic and biodegradative pathways of chlorophyll metabolism are, so far as is possible, described with some predictions as to the likely fate of the missing tonnes. Two types of degradation are recognized; the first involves up to five defined enzymes concerned with the early stages, the second covers the less well defined enzymic and non-enzymic destruction of the macrocyclic structure. These degradative reactions are compared with the reactions implicated in the breakdown of other porphyrins including haems in plants and animals. A brief description is given of the occurrence of breakdown products of chlorophyll in past biomass, including those of geological significance and those in a more recent archaeological context. Finally, the economic significance of chlorophyll breakdown is considered in the context of agriculture and horticulture, veterinary and medical sciences, food colouring and cosmetic industries, and the multi-million-dollar attraction of autumn leaf fall to tourism. Contents Summary 256 I. Introduction 256 II. Chlorophylls: global production and destruction 259 III. Chlorophylls: nomenclature and chemical characteristics 260 IV. Chlorophyll metabolism 268 V. Chlorophyll degradation during senescence 274 VI. Other degradative conditions 278 VII. Breakdown products in past biomass 287 VIII. Pathways of degradation 289 IX. Economic importance 291 Acknowledgements 294 References 294.

Photodynamic therapy in the normal rat colon with phthalocyanine sensitisation

Photodynamic therapy (PDT) involves the interaction of light with an administered photosensitising agent to produce cellular destruction. It has promising potential for the local and endoscopic treatment of gastrointestinal cancer. There is however little data on the response of normal intestine to PDT. We have investigated the use of a new photosensitiser chloro aluminum sulphonated phthalocyanine (AlSPc) for colonic PDT. The peak concentration of AlSPc in the colon measured by alkali extraction occurred 1 h after i.v. injection. The cellular uptake demonstrated by laser fluorescence microscopy was greater in the mucosa than in the muscle. AlSPc was activated in the tissues by light from an argon ion pumped dye laser at 675 nm. The laser power was set at 100 mW and the fibre placed touching the mucosa. In control animals no macroscopic damage was seen. Temperature measurement using a microthermocouple array showed no temperature rise during light exposure. The energy (fluence), dose of sensitiser and time from sensitisation to phototherapy were altered and the area of necrosis measured. The geometry of the colon made theoretical analysis of the correlation between laser energy and size of lesion difficult. However, following direct measurement of the relative light intensity (fluence rate) in the colon we were able to confirm that there was a threshold fluence for colonic necrosis. The area of photodynamic damage seen 72 h after phototherapy fell with the fall in tissue concentration of AlSPc from 1 h to 1 month after i.v. injection. However, maximum tissue necrosis occurred when treatment was performed immediately after i.v. injection. In this situation, intense vascular spasm was seen and any light transmitted through the colon which fell on the small bowel mesentery caused a lethal ischaemic necrosis. The initial histological changes after PDT were vascular, followed by full thickness necrosis at 72 h. Healing by regeneration was complete by 2-3 weeks. Despite full thickness necrosis there was no reduction in the colonic bursting pressure at any time. Colon treated by hyperthermia had a reduced bursting pressure. Specific collagen stains showed that PDT did not alter the submucosal collagen architecture whereas hyperthermia did.

A comparison of different photosensitizing dyes with respect to uptake C3H-tumors and tissues of mice

Nine dyes, all potential sensitizers for photodynamic cancer therapy (PDT), were injected in mice with C3H mammary carcinomas. Twenty-four hours later the animals were sacrificed and the dye concentrations in tumors and 9 other tissues were measured by means of spectrofluorimetry. The 9 dyes were: Photofrin II (PII), hematoporphyrin (HP)-di-hexyl-ether, PSD-007 (a sensitizer used in clinical trials in China), tetraphenyl porphine tetrasulfonate (TPPS4), tetra(3-hydroxy phenyl)porphyrin (3THPP), aluminium phthalocyanine tetrasulfonate (AlPCTS), aluminium phthalocyanine (AlPC), chlorin e6 (Chl e6) and merocyanine 540 (MC 540). The porphyrin precursor delta-aminolevulinic acid was also tested and found to induce porphyrin fluorescence in tumors and some other tissues. The best tumorlocalizer of those tested was 3THPP. This drug also showed a favorable tissue distribution. The following dyes showed lower skin/tumor concentration ratios than PII (the most widely used dye for PDT): Chl e6, PSD-007, HP-di-hexyl-ether and 3THPP. Low brain/tumor ratios were found for: PSD-007, HP-di-hexyl-ether, 3THPP, TPPS4 and AlPCTS.

The effect of localized porphyrin photodynamic therapy on the induction of tumour metastasis

Studies were performed to determine whether localized treatment of subcutaneously growing Lewis Lung Carcinoma (LLC) in C57BL/6 mice with porphyrin photodynamic therapy (PDT) affects the formation of distant metastases. Treatments consisted of a 10 mg kg-1 dose of dihematoporphyrin-ether (Photofrin II) followed 24 h later by local tumour irradiation with 630 nm red light. Total doses of light ranged from 0-500 J cm-2 and the irradiance of delivered light was 150 mW cm-2. Primary LLC tumours were treated at a volume of 25-30 mm3, and lung metastases were determined 21 days following transplantation. Mice exposed to PDT treatment which produced either partial or complete local tumoricidal responses had significantly decreased numbers of metastatic lung colonies compared to controls. In addition, PDT treated mice had equal or less metastatic lung colonies than comparable mice treated with local surgical excision of the primary LLC lesion. These results indicate that local PDT does not enhance metastatic spread of LLC following either curative or noncurative treatments.

Photodynamic therapy of C3H mouse mammary carcinoma with haematoporphyrin di-ethers as sensitizers

Haematoporphyrin di-ethers were synthesized and tested as sensitizers for photodynamic therapy of C3H/Tif mammary tumours in mice. Growth curves of the tumours were determined by measuring the tumour volume. The animals were given 25 mg porphyrins kg-1 body weight i.p. and 24 h later exposed to 135 J cm-2 of 630 nm light at a fluence rate of 150 mW cm-2. The sensitizing efficiency of the ethers was measured in terms of the increase in growth time of the treated tumours, as compared with that of untreated controls, needed to reach a volume 5 times larger than that at the time of the treatment. This sensitizing efficiency increased with decreasing polarity, i.e. in the order di-methyl ether, di-propyl ether, dibutyl ether and di-amyl ether. Haematoporphyrin di-amyl ether was more efficient than haematoporphyrin derivative and insignificantly less efficient than photofrin II (DHE). This was true for sensitization of both tumours and normal tissue.