title: Influence of a haematoporphyrin derivative on the protoporphyrin IX synthesis and photodynamic effect after 5-aminolaevulinic acid sensitization in human colon carcinoma cells.
abstract: Haematoporphyrin derivatives (HPDs) are potent sensitizers in photodynamic therapy (PDT), associated with prolonged skin photosensitivity. 5-Aminolaevulinic acid (5-ALA), a natural precusor of haem, is converted intracellularly into the photosensitive agent protoporphyrin IX (PPIX), causing direct cytotoxicity after laser light irradiation but limited skin photosensitivity over 1-2 days and higher tumour selectivity. Unfortunately, the use of 5-ALA in PDT has been shown to cause only superficial tissue necrosis. Therefore, a combination of HPD and 5-ALA could be of great clinical value in the treatment of tumours if a synergistic effect of both sensitizers on tumour cell necrosis with less skin photosensitivity could be demonstrated. Human colon adenocarcinoma cells (HT-29) were cultured with either HPD or 5-ALA alone, simultaneously for 24 h with 5-ALA and HPD or in succession with 5-ALA (18 h) followed by HPD (6 h at different concentrations. Intracellular PPIX concentrations were determined by high-performance thin-layer chromatography. Furthermore, PDT was performed with an incoherent light source (lambda = 580-740 nm) using a light dose of 30 J cm(-2) and an output power of 40 mW cm(-2). The intracellular PPIX concentration correlated well with 5-ALA drug dose and incubation time and was highest after single 5-ALA sensitization. In the presence of HPD, either simultaneously or sequentially, PPIX decreased significantly. The PDT effect after simultaneous incubation with both sensitizers for 24 h was not superior to incubation with HPD alone. If 5-ALA incubation (18 h) was followed by HPD (6 h) cytotoxicity after PDT was higher than with either single drug. 5-ALA (80 microg ml(-1)) led to a decrease in tumour cell viability by 40%. A similar effect could be observed when 5-ALA and HPD were sequentially combined allowing for a reduction of the 5-ALA dose from 80 microg ml(-1) in the absence of HPD to 60 microg ml(-1) and 5 microg ml(-1) together with 0.5 microg ml(-1) and 2 microg ml(-1) HPD respectively. We speculate that the enhanced PDT effect after the combined administration of 5-ALA and HPD to cultures of colon carcinoma cells should be even more impressive in the tumour in vivo, since HPD primarily targets the tumour microvasculature and secondarily tumour cells.
authors.affiliation: Department of Internal Medicine I, University of Regensburg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Messmann
authors.forename: M
authors.initials: M
authors.lastname: Geisler
authors.forename: U
authors.initials: U
authors.lastname: Gross
authors.forename: C
authors.initials: C
authors.lastname: Abels
authors.forename: R M
authors.initials: RM
authors.lastname: Szeimies
authors.forename: P
authors.initials: P
authors.lastname: Steinbach
authors.forename: R
authors.initials: R
authors.lastname: Knüchel
authors.forename: M
authors.initials: M
authors.lastname: Doss
authors.forename: J
authors.initials: J
authors.lastname: Schölmerich
authors.forename: A
authors.initials: A
authors.lastname: Holstege
mesh_terms: D000622:Aminolevulinic Acid / Q000494:pharmacology*; D002277:Carcinoma / Q000378:metabolism* / Q000628:therapy; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D006415:Hematoporphyrins / Q000494:pharmacology*; D006801:Humans; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011524:Protoporphyrins / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D006415:Hematoporphyrins; D017319:Photosensitizing Agents; D011524:Protoporphyrins; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX