title: Factors affecting aminolaevulinic acid-induced generation of protoporphyrin IX.
abstract: Photodynamic therapy (PDT) may cause tumour cell destruction by direct toxicity or by inducing cellular hypoxia as a result of microcirculatory shutdown. Aminolaevulinic acid (ALA) causes cellular accumulation of protoporphyrin IX (PPIX) in cells exposed to it in excess. PPIX can be used as a photosensitizer for PDT. Microcirculatory shutdown may be induced by toxicity to the endothelial and vascular smooth muscle (VSM) cells or by release of vasoactive substances. We have studied whether PPIX is produced by endothelial, VSM and tumour cells on exposure to ALA and whether these cell lines are directly damaged by PDT in vitro. Tumour endothelial cells are angiogenic and we have, therefore, investigated the effect of cellular proliferation rates on PPIX generation. Tumour cells generate more PPIX intracellularly than the non-neoplastic cell lines studied and are correspondingly more sensitive to PDT-induced cytotoxicity. Endothelial cells are sensitive to PDT-induced cytotoxicity and accumulate between 1.5 and four times more PPIX when proliferating (as during tumour-induced angiogenesis) than when quiescent. We conclude that PPIX-mediated PDT may exert some of its effects on the microcirculation of treated tissues by direct toxicity to endothelial and VSM cells, and that this toxicity may be enhanced in the tumour microenvironment.
authors.affiliation: Department of Surgical and Anaesthetic Sciences, Sheffield University, UK.
authors.forename: L
authors.initials: L
authors.lastname: Wyld
authors.forename: J L
authors.initials: JL
authors.lastname: Burn
authors.forename: M W
authors.initials: MW
authors.lastname: Reed
authors.forename: N J
authors.initials: NJ
authors.lastname: Brown
mesh_terms: D000622:Aminolevulinic Acid / Q000494:pharmacology*; D002455:Cell Division / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured / Q000528:radiation effects; D003470:Culture Media; D004730:Endothelium, Vascular / Q000166:cytology; D006801:Humans; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000528:radiation effects; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000378:metabolism*; D011524:Protoporphyrins / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays
chemical_list: D003470:Culture Media; D017319:Photosensitizing Agents; D011524:Protoporphyrins; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX