Intracellular localization is a cofactor for the phototoxicity of protoporphyrin IX in the gastrointestinal tract: in vitro study.
Photodynamic therapy (PDT) is a new treatment modality for solid tumors as well as for flat lesions of the gastrointestinal tract. Although the use of 5-aminolevulinic acid-induced protoporphyrin IX (PPIX) shows important advantages over other photosensitizers, the main mechanisms of phototoxicity induced are still poorly understood. Three human colon carcinoma cell lines with variable degrees of differentiation and a normal colon fibroblast cell line were used to generate a suitable in vitro model for investigation of photosensitizer concentration as well as the applied light dose. Also, the effects of intracellular photosensitizer localization on efficiency of PDT were examined, and cellular parameters after PDT (morphology, mitochondrial transmembrane potential, membrane integrity and DNA fragmentation) were analyzed to distinguish between PDT-induced apoptosis from necrosis. The fibroblast cell line was less affected by phototoxicity than the tumor cells to a variable degree. Well-differentiated tumor cells showed higher toxicity than less-differentiated cells. After irradiation, cell lines with cytosolic or mitochondrial PPIX localization indicate a loss of mitochondrial transmembrane potential resulting in growth arrest, whereas membrane-bound PPIX induces a loss of membrane integrity and consequent necrosis. Although the absolute amount of intracellular photosensitizer concentration plays the main determining role for PDT efficiency, data indicate that intracellular localization has additional effects on the mode of cell damage.
Krieg
René C
RC
National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
Messmann
Helmut
H
Schlottmann
Klaus
K
Endlicher
Esther
E
Seeger
Stephan
S
Schölmerich
Jürgen
J
Knuechel
Ruth
R
D000230:Adenocarcinoma / Q000188:drug therapy; D003110:Colonic Neoplasms / Q000188:drug therapy; D004064:Digestive System / Q000187:drug effects*; D006801:Humans; D010778:Photochemotherapy / Q000009:adverse effects; D017319:Photosensitizing Agents / Q000009:adverse effects*; D011524:Protoporphyrins / Q000009:adverse effects*; D014407:Tumor Cells, Cultured
D017319:Photosensitizing Agents; D011524:Protoporphyrins; C028025:protoporphyrin IX