The influence of iron chelators on the accumulation of protoporphyrin IX in 5-aminolaevulinic acid-treated cells.
Human adenocarcinoma cells of the line WiDr and Chinese hamster lung fibroblasts of the line V79 were treated with 5-aminolaevulinic acid (5-ALA) and exposed to light. The effects of the iron chelators ethylenediaminetetraacetic acid (EDTA) and desferrioxamine (DEF) were assessed. Both cell lines were treated with various concentrations of 5-ALA in the presence or absence of the iron chelators for 4 h in serum-free medium. The accumulation of protoporphyrin IX (PpIX) reached a maximum level at 1 mM 5-ALA in WiDr cells [280 ng PpIX (mg protein x 4 h-1] and at 0.1 mM 5-ALA in V79 cells [55 ng PpIX (mg protein x 4 h)-1]. PpIX was the only fluorescing porphyrin in these cells after 5-ALA treatment alone or in combination with the chelators. The iron chelators did not influence the intracellular localisation pattern of PpIX in 5-ALA-treated cells. While both chelators enhanced the accumulation of PpIX in 5-ALA-treated cells, DEF was found to be superior at equal concentrations. A linear relationship between the applied concentration of DEF and the DEF-induced increase in PpIX accumulation was observed in double-reciprocal plots. The intercepts of the regression lines with the ordinate indicate that the ferrochelatase is saturated with PpIX when the 5-ALA concentration exceeds 0.3 mM and 0.05 mM in WiDr and V79 cells respectively. The DEF-induced enhancement of PpIX accumulation in 5-ALA-treated cells was cell line and 5-ALA concentration dependent. At a 5-ALA concentration inducing a maximum level of PpIX accumulation, inhibition of ferrochelatase activity enhanced the PpIX accumulation 3- and 1.4-fold in V79 and WiDr cells respectively. The relative gain in PpIX accumulation increased with decreasing concentration of 5-ALA. In cells treated with the lowest concentrations of 5-ALA used in this study, DEF enhanced PpIX accumulation 44- and 3.5-fold in V79 and WiDr cells respectively. The iron chelator-induced increase in cellular PpIX accumulation was followed by a similar increase in sensitivity to photoinactivation. The ferrochelatase inhibitor dihydropyridine 3,5-diethoxycarbonyl-1,4-dihydrocollidine reduced the accumulation of PpIX in both cell lines.
Berg
K
K
Institute for Cancer Research, Department of Biophysics, Montebello, Norway.
Anholt
H
H
Bech
O
O
Moan
J
J
D000230:Adenocarcinoma / Q000188:drug therapy / Q000378:metabolism; D000622:Aminolevulinic Acid / Q000494:pharmacology* / Q000627:therapeutic use; D000818:Animals; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003997:Dicarbethoxydihydrocollidine / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007502:Iron Chelating Agents / Q000494:pharmacology*; D008856:Microscopy, Fluorescence; D063086:Organothiophosphates / Q000494:pharmacology*; D017319:Photosensitizing Agents / Q000378:metabolism*; D011524:Protoporphyrins / Q000032:analysis / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism
D007502:Iron Chelating Agents; D063086:Organothiophosphates; D017319:Photosensitizing Agents; D011524:Protoporphyrins; C006863:butyl phosphorotrithioate; D003997:Dicarbethoxydihydrocollidine; D000622:Aminolevulinic Acid; D004492:Edetic Acid; C028025:protoporphyrin IX