Photodynamic therapy induced cell death of hormone insensitive prostate cancer PC-3 cells with autophagic characteristics.

BACKGROUND: The introduction of photodynamic therapy (PDT) to the treatment of advanced prostate cancer can accomplish the eradication of local neoplasm and distant metastases with minimized damage to the adjacent structures. The evidence of PDT efficacy for androgen-refractory prostate cancer will be especially meaningful for the patients resistant to hormone therapy.
METHODS: Pheophorbide a (PhA) as a photosensitizer was employed to evaluate the photodynamic efficacy in androgen-insensitive PC-3 prostate cancer cells in culture by cell viability assay, reactive oxygen species (ROS) measurement and cell cycle test. Characteristics of apoptosis and autophagy were investigated via DNA fragmentation electrophoresis and immune-fluorescence staining, acidic vesicle determination and detection of LC3B in puncta form by fluorescence microscopy, Western blotting of autophagy-related (Atg) proteins and detailed phenotype shown by electron microscopy.
RESULTS: PhA exerted significant photo-cytotoxicity toward androgen-insensitive prostate cancer PC-3 cells in photosensitizer-dose and light-dose dependent manners. The photoactivation immediately initiated hyperproduction of ROS, the depolarization of mitochondrial membrane potential and the arrest of the cell cycle in the G0/G1 phase. Autophagy was revealed in PhA-PDT treated PC-3 cells by a significant high amount of acidic vesicular organelles with acridine orange staining, recruitment of LC3B on the membrane of autophagosomes by fluorescent microscopy, double membrane-bound vesicles suggesting autophagosomes by electron microscopy, significant increased Atg proteins such as beclin-1, Atg12-Atg5 conjugation, Atg7 and the conversion of LC3B-I to LC3B-II by Western blot analysis.
CONCLUSIONS: PhA-mediated PDT induced significant autophagy in hormone-refractory prostate cancer PC-3 cells.