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|Title:||Apoptosis and porphyrin biosynthesis by a photodynamic chemotherapeutic|
|Doctoral Committee Chair(s):||Kelley, Keith W.|
|Department / Program:||Animal Sciences|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
Health Sciences, Immunology
Health Sciences, Oncology
|Abstract:||$\delta$-Aminolevulinic acid (ALA) causes transformed cells to accumulate protoporphyrin IX (Proto). Subsequent exposure to light in vitro causes intracellular Proto to initiate formation of singlet oxygen molecules, leading to self-destruction. This photo-activated destruction by ALA is enhanced by addition of the tetrapyrrole modulator 1,10-phenanthroline (Oph), by enhancing Proto accumulation. We determined the efficacy and intracellular localization and biosynthesis of Proto, and the role of apoptosis in ALA- and Oph-mediated cell death of transformed cells.
Methylcholanthrene-induced sarcoma (Meth-A) solid tumors exhibited a synergistic accumulation of Proto when Oph was used in conjunction with ALA. The use of ALA and Oph-based photo-treatment in mice bearing Meth-A solid tumors resulted in necrosis of tumors in 5 of 6 mice, as determined by both a significant reduction in size and histopathology, with little damage to surrounding normal tissue. Some inflammation of the skin was evident after photo-therapy, due to singlet-oxygen mediated cell death of the tumor.
The intracellular localization and pathway of porphyrin biosynthesis in transformed cells was investigated. Proto synthesis occurs in the mitochondria and cytoplasm, but neither the transport of pyrroles and porphyrins, nor the location of all the heme-synthesizing enzymes, have been established. We determined that the conversion of ALA to Coprogen occurs in the cytoplasm of MLA 144 cells. We also show that conversion of Coprogen to Proto by isolated MLA 144 mitochondria is an ATP-dependent process. Transport of Coprogen into mitochondria may involve the mitochondrial peripheral-type benzodiazepine receptor (M-PBR).
Survival of WEHI 164 and MLA 144 cells declines significantly after 18 h treatment with ALA and Oph in darkness. Oph and Proto, but not ALA, induce growth arrest. After 3 h of incubation Oph, but not Proto or ALA, induce internucleosomal cleavage of DNA, characteristic of apoptosis, in MLA 144 cells. Apoptosis induction appears to be cell cycle dependent, since cells accumulate in early S phase, with little or no cells in G0/G1 phase, indicative of cell-cycle dependent apoptosis. Oph-induced apoptosis was abrogated (75%) by cycloheximide. These results indicate that Oph induces growth arrest and apoptosis in transformed cells.
|Rights Information:||Copyright 1996 Rebeiz, Natalie|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9702649|