title: Targeting PBR by hexaminolevulinate-mediated photodynamic therapy induces apoptosis through translocation of apoptosis-inducing factor in human leukemia cells.
abstract: Photodynamic therapy (PDT) with endogenous protoporphyrin IX derived from 5-aminolevulinic acid or its derivatives has been established for treatments of several premalignancies and malignancies; however, the mechanism of the modality is not fully elucidated. The mitochondrial permeability transition pore consists mainly of the mitochondrial outer membrane voltage-dependent anion channel and the peripheral benzodiazepine receptor (PBR) and the mitochondrial inner membrane adenine nucleotide translocator (ANT). These mitochondrial proteins are responsible for the permeability transition that leads to apoptosis. In the present study, the human leukemia cell line, Reh, was treated with PDT using hexaminolevulinate (HAL). More than 80% of apoptotic Reh cells were found after HAL-mediated PDT (HAL-PDT) with high-molecular-weight (50 kbp) DNA fragmentation. Addition of PK11195 or Ro5-4864, two ligands of PBR, during HAL-PDT significantly inhibited the apoptotic effect. Bongkrekic acid, a ligand for ANT, also reduced the PDT effect. Although the mitochondrial transmembrane potential collapsed, neither cytosolic translocation of mitochondrial cytochrome c nor activation of caspase-9, caspase-8, caspase-3, and poly(ADP-ribose) polymerase were found. However, nuclear translocation of mitochondrial apoptosis-inducing factor (AIF) was shown by both immunoblotting and immunocytochemistry. Because AIF is the sole one among all proapoptotic factors involved in caspase-dependent and caspase-independent pathways that induces the high-molecular-weight DNA fragmentation, we conclude that HAL-PDT specifically targets PBR, leading to apoptosis of the Reh cells through nuclear translocation of mitochondrial AIF. This study suggests PBR as a possible novel therapeutic target for HAL-based PDT of cancer.
authors.affiliation: Department of Pathology, The Norwegian Radium Hospital, University of Oslo, Oslo, Norway.
authors.forename: Ingegerd Eggen
authors.initials: IE
authors.lastname: Furre
authors.forename: Susan
authors.initials: S
authors.lastname: Shahzidi
authors.forename: Zivile
authors.initials: Z
authors.lastname: Luksiene
authors.forename: Michael T N
authors.initials: MT
authors.lastname: Møller
authors.forename: Elin
authors.initials: E
authors.lastname: Borgen
authors.forename: Janet
authors.initials: J
authors.lastname: Morgan
authors.forename: Kinga
authors.initials: K
authors.lastname: Tkacz-Stachowska
authors.forename: Jahn M
authors.initials: JM
authors.lastname: Nesland
authors.forename: Qian
authors.initials: Q
authors.lastname: Peng
mesh_terms: D000622:Aminolevulinic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D051033:Apoptosis Inducing Factor / Q000378:metabolism*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D045304:Cytochromes c / Q000502:physiology; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D007945:Leukemia, Lymphoid / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011524:Protoporphyrins / Q000096:biosynthesis* / Q000378:metabolism; D018079:Receptors, GABA / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: C494829:AIFM1 protein, human; D051033:Apoptosis Inducing Factor; D017319:Photosensitizing Agents; D011524:Protoporphyrins; D018079:Receptors, GABA; C499229:TSPO protein, human; D000622:Aminolevulinic Acid; D045304:Cytochromes c; C028025:protoporphyrin IX; C419924:5-aminolevulinic acid hexyl ester