Mechanism of colon cancer cell apoptosis mediated by pyropheophorbide-a methylester photosensitization

Abstract

Pyropheophorbide-a methylester (PPME) is a second generation of photosensitizers used in photodynamic therapy (PDT). We demonstrated that PPME photosensitization triggered apoptosis of colon cancer cells as measured by using several classical parameters such as DNA laddering, PARP cleavage, caspase activation and mitochondrial release of cytochrome c. Preincubation of cells with N-acetyl cysteine (NAC) or pyrolidine dithiocarbamate (PDTC) protected against apoptosis mediated by PPME photosensitization showing that reactive oxygen species (ROS) are involved as second messengers. On the other hand, photosensitization carried out in the presence of deuterium oxide (D 2 O) which enhances singlet oxygen ( 1 O 2 ) lifetime only increases necrosis without aecting apoptosis. Since PPME was localized in the endoplasmic reticulum (ER)/Golgi system and lysosomes, other messengers than ROS were tested such as calcium, Bid, Bap31, phosphorylated Bcl-2 and caspase-12 but none was clearly identi®ed as being involved in triggering cytochrome c release from mitochondria. On the other hand, we demonstrated that the transduction pathways leading to NF-kB activation and apoptosis were clearly independent although NF-kB was shown to counteract apoptosis mediated by PPME photosensitization. Oncogene (2001) 20, 4070 ± 4084.

Physical and chemical properties of pyropheophorbide-a methyl ester in ethanol, phosphate buffer and aqueous dispersion of small unilamellar dimyristoyl-l-α-phosphatidylcholine vesicles

“…In view of its potential use in the PDT of cancer, pyropheophorbide-a methyl ester (PPME) is an attractive second-generation photosensitizer 12,13,14 . The structure of PPME differs from that of chlorophyll-a ( Fig.1) in the loss of the magnesium in the center of the molecule, the substitution of the phytol group (H 39 C 20 ) by methyl (CH 3 ) and the loss of a carbomethoxy group (-COOCH 3 ) at C 10 of the isocyclic ring.…”

pH-dependent Interaction of Cytochrome c with Mitochondrial Mimetic Membranes

“…Events that lead to cellular oxidative stress and loss of mitochondrial membrane potential, such as Ca 2ϩ -induced permeability transition or photodynamic therapy, are known inducers of apoptosis and cyt c release (3)(4)(5)(6)(7)(8)(9)(10)(11)(12).…”

Optimizing photodynamic therapy by liposomal formulation of the photosensitizer pyropheophorbide-a methyl ester: In vitro and ex vivo comparative biophysical investigations in a colon carcinoma cell line

“…12 It was found that PPME is present inside every organelle (endoplasmic reticulum, Golgi, lysosomes and mitochondria). By contrast, Matroule et al 14 have reported that 0.25 mM PPME does not localize in the HCT-116 mitochondria. We have re-examined the co-localization of PPME with HCT-116 mitochondria with a larger range of PPME concentrations; the drug being administrated as a free molecule or encapsulated in liposomes.…”

“…13, 14 The type of cell mortality induced by PPME, correlated with its intracellular localization, has been intensively studied by Matroule 13, 14 and Sun. 12 These authors found discordance in the localization of PPME within mitochondria in the cell lines investigated, HCT-116 and NCI-h446.…”