Abstract

The objective of this study was to characterize the death mechanism of human epidermoid carcinoma cells (A431) triggered by photodynamic therapy (PDT) with pheophorbide a . First of all, significant inhibition on the survival of A431 cells (< 20 %) was observed when an irradiation dose of 5.1 J/cm2 combined with 125 ng/ml of pheophorbide a was applied. Survival rate of human keratinocyte cells was over 70 % under the same PDT parameters, suggesting that pheophorbide a killed cancer cells selectively. Mitochondria were the main target sites where pheophorbide a accumulated. Formation of reactive oxygen species (ROS) was detected after PDT. Addition of antioxidant N-Acetyl cysteine prevented ROS production and increased cell survival thereafter. The decrease in cellular ATP level was also observed at 6 hrs after PDT. Typical apoptotic cellular morphology and a collapse of mitochondrial membrane potential occurred after PDT. The loss of mitochondrial membrane potential led to the release of cytochrome c from the mitochondria to the cytosol, followed by activation of caspase-9 and caspase-3. The activation of caspase-3 resulted in poly(ADP-ribose) polymerase (PARP) cleavage in A431 cells, followed by DNA fragmentation. In conclusion, the results demonstrated that pheophorbide a possessed photodynamic action against A431 cells, mainly through apoptosis mediated by mitochondrial intrinsic pathway triggered by ROS.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

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