Evidence that photoactivated pheophorbide a causes in human cancer cells a photodynamic effect involving lipid peroxidation.
Photodynamic therapy (PDT) is a treatment modality that uses a combination of a photosensitizer and light to induce a photokilling process in the tumor tissue. Recently we re-considered pheophorbide a (Pba), a second-generation photosensitizer that has not yet been thoroughly investigated. Here, we report that Pba irradiated at 14 J/cm(2) induces a strong photodynamic effect in four tumor cell lines, with IC(50) values ranging between 70 and 250 nM. The mechanism of phototoxicity has been investigated in HeLa (IC(50) = 150 nM) and HepG2 (IC(50) = 95 nM) cells. In both cell lines Pba induces lipid peroxidation, as indicated by a marked increase of malonyldialdehyde and oxidized C11 BODIPY(581/591). At high doses (>IC(50)), Pba arrests cell growth completely by activating apoptosis and/or necrosis, while at low doses (<IC(50)), the photosensitizer causes a temporary growth arrest. In the presence of Pba photodamage, the cells activate a protective mechanism against oxidative stress mediated by a strong increase of heme oxygenase-1 expression (up to 12-fold in HepG2 and 25-fold in HeLa). Moreover, considering that GSTA1-1 is a response gene to lipid peroxidation, we treated with Pba a genetically modified HepG2 clone, in which GSTA1-1 was constitutively silenced by siRNA, observing a 25% increase of lipid peroxidation as compared to HepG2 clone expressing GSTA1-1. These data suggest that combine treatments in which Pba is used with gene-silencing molecules against HO-1 and GSTA1-1 should potentiate PDT.
Department of Biomedical Science and Technology, School of Medicine, Udine, Italy.
Valentina
V
Rapozzi
Mara
M
Miculan
Luigi E
LE
Xodo
D017209:Apoptosis / Q000187:drug effects; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D045744:Cell Line, Tumor / Q000187:drug effects; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000528:radiation effects; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D006367:HeLa Cells / Q000187:drug effects; D051547:Heme Oxygenase-1 / Q000502:physiology; D006801:Humans; D020128:Inhibitory Concentration 50; D015227:Lipid Peroxidation / Q000187:drug effects; D008113:Liver Neoplasms / Q000473:pathology; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D018384:Oxidative Stress; D010778:Photochemotherapy; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000494:pharmacology; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology* / Q000528:radiation effects
D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; D011838:Radiation-Sensitizing Agents; D002734:Chlorophyll; C496541:HMOX1 protein, human; D051547:Heme Oxygenase-1; C484555:GSTA1 protein, human; D005982:Glutathione Transferase; C032623:pheophorbide a