PH-DEPENDENT FORMATION OF 5-AMINOLEVULINIC ACID-INDUCED PROTOPORPHYRIN-IX IN FIBROSARCOMA CELLS

pH-Dependent variations in the fluorescence intensity of 5-aminolaevul inic acid-induced 5-aminolaevulinic acid protoporphyrin IX (PP IX) wer e compared with the cell viability following light irradiation. The fl uorescence intensity was determined by flow cytometry and the cell act ivity was investigated by a colorimetric 3-(4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide (MTT) assay 24 h after photodynamic t reatment. The results obtained by fluorescence measurements clearly sh owed that pH values of the incubation medium containing (5-ALA) below and above pH 7.4 led to a significant decrease in the fluorescence int ensity. The viability of cells incubated with 0.6 mM 5-ALA in a medium at pH 6.0 was unaffected on exposure to light at lambda = 635 nm up t o 15 J cm(-2). However, cells incubated at pH 7.3 (with the other trea tment parameters the same) were nearly completely destroyed. In additi on, depletion of intracellular PP IX was faster in physiological mediu m than in acidic medium. (C) 1997 Elsevier Science S.A.