Is delta-aminolevulinic acid dehydratase rate limiting in heme biosynthesis following exposure of cells to delta-aminolevulinic acid?
Understanding the regulation and control of heme/porphyrin biosynthesis is critical for the optimization of the delta-aminolevulinic-acid (ALA)-mediated photodynamic therapy of cancer, in which endogenously produced protoporphyrin IX (PPIX) is the photosensitizer. The human breast cancer cell line MCF-7, the rat mammary adenocarcinoma cell line R3230AC, the mouse mammary tumor cell line EMT-6 and the human mesothelioma cell line H-MESO-1 were used to study ALA-induced PPIX levels and their relationship to delta-aminolevulinic acid dehydratase (ALA-D) activity in vitro. Incubation of these cell lines with 0.5 mM ALA for 3 h resulted in a significant increase in PPIX accumulation, compared with control cells, but there was no significant change in ALA-D activity. Exposure of cells incubated with ALA to 30 mJ/cm2 of fluorescent light, a dose that would cause a 50% reduction in cell proliferation, did not significantly alter the activity of ALA-D. Increasing the activity of porphobilinogen deaminase (PBGD), the enzyme immediately subsequent to ALA-D, by four- to seven-fold via transfection of cells with PBGD complementary DNA did not alter the activity of ALA-D. However, incubation of cells with various concentrations of succinyl acetone, a potent inhibitor of ALA-D, caused a concomitant decline in both PPIX accumulation and ALA-D activity. These data imply that when cells are exposed to exogenous ALA, ALA-D is an important early-control step in heme/porphyrin biosynthesis and that regulation of PPIX synthesis by this dehydratase may impact the effectiveness of ALA-mediated photosensitization.
Gibson
S L
SL
Department of Biochemistry and Biophysics, Box 712, University of Rochester School of Medicine and Dentistry, 601 Elmwood Avenue, Rochester, NY 14642, USA.
Havens
J J
JJ
Metz
L
L
Hilf
R
R
D000622:Aminolevulinic Acid / Q000494:pharmacology*; D000818:Animals; D006418:Heme / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D051379:Mice; D017319:Photosensitizing Agents / Q000494:pharmacology*; D000623:Porphobilinogen Synthase / Q000378:metabolism*; D051381:Rats; D014407:Tumor Cells, Cultured
D017319:Photosensitizing Agents; D006418:Heme; D000622:Aminolevulinic Acid; D000623:Porphobilinogen Synthase