Photodynamic therapy-induced death of MCF-7 human breast cancer cells: a role for caspase-3 in the late steps of apoptosis but not for the critical lethal event.

Abstract

Photodynamic therapy (PDT) causes mitochondrial damage and induces apoptosis through release of cytochrome c and activation of caspase-3. To test whether caspase 3 is the sole executioner of apoptosis and its role in overall cell lethality, we compared the response of MCF-7c3 cells that express a stably transfected CASP-3 gene to that of parental MCF-7:SW8 cells transfected with vector alone (MCF-7v). Following photosensitization with the phthalocyanine Pc 4 and red light, cytochrome c was released from the mitochondria to equivalent extents in the two cell lines. However, the appearance of apoptotic indicators, such as active caspase-3 (DEVDase), cleavage of poly(ADP-ribose) polymerase, and oligonucleosomal DNA fragmentation, was observed only in MCF-7c3 cells during the first 6 h after photosensitization. Although production of 50-kb DNA fragments and chromatin condensation were found in PDT-treated MCF-7v cells by 20-24 h posttreatment, the rate and extent of apoptosis were much less than in MCF-7c3 cells. MCF-7c3 cells were more sensitive to photosensitization than were MCF-7v cells when assayed for loss of viability by reduction of a tetrazolium dye. However, the two cell lines were equally sensitive to photodynamic killing when evaluated by a clonogenic assay. These results show (a) the importance of assessing overall cell death by clonogenic assay; (b) that the critical lethal event is independent of caspase-3, perhaps at or near the release of cytochrome c from mitochondria; and (c) that the caspase-3-mediated events appear to be irrelevant in determining overall killing of cells.

• Authors: L Y Xue, S M Chiu, N L Oleinick
• Journal: Experimental cell research (Exp Cell Res) Vol. 263 Issue 1 Pg. 145-55 (Feb 01 2001) ISSN: 0014-4827 [Print] United States
• PMID: 11161713 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Cytochrome c Group
• Indoles
• Photosensitizing Agents
• phthalocyanine Pc 4
• Poly(ADP-ribose) Polymerases
• CASP3 protein, human
• CASP9 protein, human
• Caspase 3
• Caspase 9
• Caspases

Topics

• Apoptosis
• Blotting, Western
• Breast Neoplasms
• Caspase 3
• Caspase 9
• Caspases (genetics, metabolism)
• Cell Size
• Cytochrome c Group (metabolism)
• DNA Fragmentation
• Dose-Response Relationship, Drug
• Enzyme Activation
• Female
• Flow Cytometry
• Humans
• In Situ Nick-End Labeling
• Indoles (pharmacology)
• Microscopy, Fluorescence
• Mitochondria (metabolism)
• Photochemotherapy
• Photosensitizing Agents (pharmacology)
• Poly(ADP-ribose) Polymerases (metabolism)
• Transfection
• Tumor Cells, Cultured