Initiation of Apoptosis versus Necrosis by Photodynamic Therapy with Chloroaluminum Phthalocyanine

Abstract

While chloroaluminum phthalocyanine is a highly effective photosensitizer of murine leukemia P388 or L1210 cells, the mode of cell death varies as a function of the PDT dose. When cells were incubated with 0.3 microM of the sensitizer, a light dose of 45 mJ cm-2 (670 +/- 5 nm) yielded a 90% apoptotic cell population within 60 min. The sensitizer localized throughout the cytoplasm and catalyzed both lysosomal and mitochondrial photodamage at this light dose. Higher light doses yielded progressively more membrane photodamage and inhibited the apoptotic response as determined by the examination of Höchst dye HO 33342-labeled nuclei, DNA fragmentation on gels and a poly(adenosylribose) polymerase (PARP)-cleavage assay. Pulse-field gel electrophoresis revealed nonspecific DNA degradation to particles > or = 50 kbp at the higher PDT doses but neither PARP cleavage nor apoptotic nuclei.

Intracellular signaling mechanisms in photodynamic therapy

“…The cell genotype and the PDT dose were also found to determine whether cell death occurs by apoptosis or necrosis [17 -28]. Indeed, apoptosis was the predominant mode of cell death when murine leukemia P388 cells were photosensitized with chloroaluminum phthalocyanine (AlPc), using low light doses, whereas necrosis was observed for higher light doses [18]. Similar results were obtained in studies where human bladder carcinoma HT1197 cells were subjected to 5-aminolevulinate (ALA)-induced PDT [24] and in CNE2 cells, TWO-1 cells (human nasopharyngeal carcinoma cells) and AY-27 cells (chemically-induced rat bladder carcinoma cells) sensitized with hypericin [23,25].…”

“…Also, expression of CrmA did not affect the kinetics of cytochrome C release Jurkat human lymphoma T cells [295] and procaspase-3 cleavage in a rat/mouse T cell hybridoma sensitized with hypericin [68], suggesting that caspase-8 does not play a major role in the demise process in this model. The activation of caspases in photosensitized cells leads to the cleavage of a number of other cell proteins, including Bap-31 (shuttle protein between the ER and the intermediate compartment and/or Golgi complex [71]), DNA-dependent protein kinase (catalytic subunit) (DNA-PK CS [75]), ICAD (inhibitor of caspase activated DNAse); prevents DNA fragmentation via binding to caspase-activated deoxyribonuclease [76]), focal adhesion kinase (FAK, a kinase involved in the regulation of cell adhesion [73]), lamins (structural components of the nuclear envelope [73]), PARP (poly(ADP-ribose) polymerase, a DNA repair enzyme [18,20,44,54,68,71,72,75,[77][78][79][80][81][82][83][84][85]) and Ras GTPase-activating protein (Ras-GAP, a negative regulator of the Ras signaling pathway [71]). DNA fragmentation in segments that are multiples of 180 -200 bp, another hallmark of apoptotic cell death [86], was also observed in PDT, using different cell types and sensitizers (Table 1).…”

Dissociation of mitochondrial depolarization from cytochrome c release during apoptosis induced by photodynamic therapy

“…PDT is a treatment for cancer and other abnormal tissue that employs a photosensitizer and visible light to produce singlet oxygen and other reactive oxygen species (Weishaupt et al, 1976), which cause an oxidative stress in cells and membrane damage (Moan and Berg, 1992) and eventually leads to cell death and tumour ablation (reviewed in Dougherty, 1993;Dougherty et al, 1998). PDT with photosensitizers that localize in the mitochondria induces rapid apoptosis (Agarwal et al, 1991;Dougherty, 1993;He et al, 1994;Luo et al, 1996;Luo and Kessel, 1997;Dougherty et al, 1998;Oleinick and Evans, 1998), probably because the photochemical damage directly targets mitochondria (Kessel and Luo, 1998) to elicit the rapid release of cytochrome c that initiates caspase-9 activation, subsequent steps in the caspase cascade, and morphological apoptosis (Kroemer et al, 1997;Granville et al, 1998Granville et al, , 1999Kessel and Luo, 1999;Varnes et al, 1999). Data in the present study show that mitochondrial depolarization caused by PDT is dose dependent, and PDT-induced cytochrome c release and apoptosis can occur in the absence of major loss of the ∆ψ m .…”

Protein kinase C inhibits singlet oxygen-induced apoptosis by decreasing caspase-8 activation

“…This therapy involves the use of a photosensitizer, which is activated by visible light locally and subsequently causes tumor ablation within a few days. After PDT in vivo, there is an evidence for both apoptosis and necrosis in tumor biopsies (Agarwal et al, 1996;Webber et al, 1996;Zaidi et al, 1993), while apoptosis is a prominent form of cell death in response to PDT of cultured cells (Agarwal et al, 1991;He et al, 1994;Luo and Kessel, 1997). PDT activates many signaling pathways that have been characterized as responses to other oxidative stresses.…”