Summary 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 aluminium sulphonated phthalocyanine (AlSPc) for colonic PDT. The peak concentration of AISPc 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 675nm. The laser power was set at lOOmW 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 72h after phototherapy fell with the fall in tissue concentration of AISPc from I 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.Photodynamic therapy (PDT) offers the potential of selectively destroying malignant tumours. Several photosensitising agents are retained longer in tumours and rapidly growing tissues than in the surrounding normal tissue. Illumination of the tumour with light of wavelengths absorbed by these agents results in tumour cell destruction (Doiron & Gomer, 1984). In spite of the potential of this technique there are certain disadvantages in the presently most widely used photosensitiser, haematoporphyrin derivative (HpD). It is a complex mixture of porphyrins whose composition varies with differing preparations and time in storage. Efforts have been directed at identifying the active component and it has been variously described as dihaematoporphyrin ether (Dougherty et al., 1984) or...

No abstract

No abstract

No abstract

No abstract