title: The centrality of PBGD expression levels on ALA-PDT efficacy.
abstract: Successful 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT) is dependent on efficient porphyrin synthesis in the inflicted cancer tissue, which is regulated by several enzymes. Irradiation of the tumor excites the light-sensitive porphyrins and results in ROS production and cell death. In this study we investigated the effect of the expression levels of two main enzymes in heme biosynthesis, ALA dehydratase (ALAD) and porphobilinogen deaminase (PBGD), on the capacity of K562 cells to undergo cell death following ALA-PDT. We manipulated PBGD and ALAD expression levels by shRNAs and PBGD overexpressing plasmid. PBGD down-regulation induced an elevation in ALAD activity, while overexpression of PBGD reduced ALAD activity, indicating a novel regulation feedback of PBGD on ALAD activity. This feedback mechanism enabled partial PpIX synthesis under PBGD silencing, whereas ALAD silencing reduced PpIX production to a minimum. ALA-PDT efficacy was directly correlated to PpIX levels. Thus, only ALAD-silenced cells were not affected by ALA+ irradiation, while following PBGD silencing, the accumulated PpIX, though decreased, was sufficient for successful ALA-PDT. The alterations in ALAD activity level initiated by changes in PBGD expression indicates PBGD's central role in heme synthesis. This enables efficient ALA-PDT, even when PBGD is not fully active. Conversely, ALAD loss resulted in reduced PpIX synthesis and consequently failure in ALA-PDT, due to the absence of compensation mechanism for ALAD.
authors.affiliation: Microscopy Unit, Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, 52900, Israel. malikz@mail.biu.ac.il
authors.forename: Avital
authors.initials: A
authors.lastname: Schauder
authors.forename: Tamar
authors.initials: T
authors.lastname: Feuerstein
authors.forename: Zvi
authors.initials: Z
authors.lastname: Malik
mesh_terms: D000622:Aminolevulinic Acid / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D011163:Hydroxymethylbilane Synthase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020014:K562 Cells; D004915:Leukemia, Erythroblastic, Acute / Q000188:drug therapy / Q000201:enzymology; D008027:Light; D010778:Photochemotherapy; D000623:Porphobilinogen Synthase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011524:Protoporphyrins / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism
chemical_list: D011524:Protoporphyrins; D034741:RNA, Small Interfering; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX; D011163:Hydroxymethylbilane Synthase; D000623:Porphobilinogen Synthase