Phototoxic reaction and porphyrin fluorescence in skin after topical application of methyl aminolaevulinate.

BACKGROUND: Photodynamic therapy using topical methyl aminolaevulinate (MAL) is a new treatment modality for skin disorders. MAL is metabolized into endogenous porphyrins, which act as photosensitizers when illuminated. OBJECTIVES: To evaluate the severity and duration of skin photosensitivity after MAL application, and to investigate its relation to the presence of endogenous porphyrins. METHODS: Placebo and 160 mg g(-1) MAL creams were randomly assigned to contralateral sites located at the forearms and fingertips of 16 healthy volunteers and were applied for 3 h. The porphyrin content in the skin was monitored by in situ fluorescence measurements following cream removal. Phototoxic reaction was evaluated after exposure to a high dose of red light. RESULTS: The porphyrin fluorescence in forearm skin peaked about 1 h after the cream removal, was halved after 8 h, and was reduced by > 90% within 24 h. Most forearm sites were photosensitive at 1 and 8 h following cream removal. Six subjects were still sensitive at 24 h, and at this time point the phototoxicity was coincidental with residual porphyrin fluorescence. In general, all reactions were mild or moderate, and included pain, erythema, oedema and transient hyperpigmentation. No photosensitivity or porphyrin fluorescence was detected at 48 h. At the fingertips photosensitivity was absent except for sporadic cases of mild pain. CONCLUSIONS: Topical MAL application and exposure to red light induced mild and moderate phototoxicity. The photosensitivity ceased within 24-48 h after cream removal, and its duration was associated with the degradation of porphyrins.

Porphyrin-related photosensitizers for cancer imaging and therapeutic applications.

A photosensitizer is defined as a chemical entity, which upon absorption of light induces a chemical or physical alteration of another chemical entity. Some photosensitizers are utilized therapeutically such as in photodynamic therapy (PDT) and for diagnosis of cancer (fluorescence diagnosis, FD). PDT is approved for several cancer indications and FD has recently been approved for diagnosis of bladder cancer. The photosensitizers used are in most cases based on the porphyrin structure. These photosensitizers generally accumulate in cancer tissues to a higher extent than in the surrounding tissues and their fluorescing properties may be utilized for cancer detection. The photosensitizers may be chemically synthesized or induced endogenously by an intermediate in heme synthesis, 5-aminolevulinic acid (5-ALA) or 5-ALA esters. The therapeutic effect is based on the formation of reactive oxygen species (ROS) upon activation of the photosensitizer by light. Singlet oxygen is assumed to be the most important ROS for the therapeutic outcome. The fluorescing properties of the photosensitizers can be used to evaluate their intracellular localization and treatment effects. Some photosensitizers localize intracellularly in endocytic vesicles and upon light exposure induce a release of the contents of these vesicles, including externally added macromolecules, into the cytosol. This is the basis for a novel method for macromolecule activation, named photochemical internalization (PCI). PCI has been shown to potentiate the biological activity of a large variety of macromolecules and other molecules that do not readily penetrate the plasma membrane, including type I ribosome-inactivating proteins, immunotoxins, gene-encoding plasmids, adenovirus, peptide-nucleic acids and the chemotherapeutic drug bleomycin. The background and present status of PDT, FD and PCI are reviewed.

Bystander effects in cell death induced by photodynamic treatment UVA radiation and inhibitors of ATP synthesis.

Confluent layers of MDCK II cells were treated with four different photosensitizers (a purified version of hematoporphyrin derivative [Photofrin], tetra(3-hydroxyphenyl)porphine [3-THPP], meso-tetra(4-sulphonatophenyl)porphine [TPPS4] and ALA-induced Protoporphyrin IX) and irradiated with blue light, with UVA without exogenous photosensitizers, or incubated with the metabolic inhibitors carbonyl cyanide m-chlorophenylhydrazone and 2-deoxy-D-glucose. Necrotic and apoptotic cells were detected about 4 h later by fluorescence microscopy. Dead cells appeared in distinct clusters in the confluent layers. The number of dead cells in these clusters was determined by manual counting and image analysis. Forty-one of the 43 experimental distributions of dead cells in clusters were found to be significantly different from a Monte Carlo simulation of the distribution of independently inactivated cells. However, a Monte Carlo simulation model, assuming that each dead cell increased the probability of inactivation of adjacent cells, fitted 34 of the 43 observed distributions of dead cells in clusters, indicating a significant bystander effect for all the investigated treatments. The bystander-effect model parameter, defined as a cell's increase in probability of dying when it has dead neighbors, was significantly lower for 3-THPP-PDT and TPPS4-PDT than for Photofrin-PDT, ALA-PDT and treatment with metabolic inhibitors.

Photodynamic therapy of superficial basal cell carcinoma with 5-aminolevulinic acid with dimethylsulfoxide and ethylendiaminetetraacetic acid: a comparison of two light sources.

The aim of this prospective randomized study was to compare the clinical and cosmetic outcome of superficial basal cell carcinomas (BCC), using either laser or broadband halogen light, in photodynamic therapy with topical 5-aminolevulinic acid (ALA). A total of 83 patients with 245 superficial BCC were included in the study. Standard treatment involved 15 min of local pretreatment with 99% dimethylsulfoxide (DMSO) before topical application of 20% ALA with DMSO (2%) and ethylendiaminetetraacetic acid (2%) as cofactors for 3 h before light exposure with either laser or a broadband lamp (BL). A complete response was achieved in 95 lesions (86%) in the laser group and 110 lesions (82%) in the BL group 6 months after treatment. Of these, 80 lesions (84%) in the laser group and 101 lesions (92%) in the lamp group were independently evaluated to have an excellent or good cosmetic post-treatment score. No serious adverse events were reported. This study shows that there is no statistical significant difference in cure the rate (P = 0.49) and the cosmetic outcome (P = 0.075) with topical application of a modified ALA-cream between light exposure from a simple BL with continuous spectrum (570-740 nm) or from a red-light laser (monochromatic 630 nm). Cost and safety are further elements in favor of the BL in this setting.