Single Cell FRET Imaging for Determination of Pathway of Tumor Cell Apoptosis Induced by Photofrin-PDT

Apoptosis is an important cellular event that plays a key role in pathogeny and therapy ofmany diseases. Apoptosis has been associated with photodynamic therapy (PDT) and itspathway is important in the mechanistic study of PDT. We show that single cell fluorescentimaging can be used to determine the pathway of PDT- induced tumor cell apoptosis. In thisstudy, ASTC-a-1 tumor cells transfected by plasmid DNA SCAT3 were treated by Photofrin-PDT.The intracellular distribution of Photofrin was observed using a confocal microscope. Theactivations of caspase-3 and caspase-8 were dynamically observed using fluorescence resonanceenergy transfer (FRET). Our experimental results show that the Photofrin molecules arelocalized in cell mitochondria, and that after PDT caspase-3 was activated rapidly whilecaspase-8 remained inactive. These results demonstrate that the tumor cell apoptosis inducedby Photofrin-PDT was directly initiated from the mitochondrial pathway.