Chapter 9: PDT: Death and Survival Pathways

Photodynamic therapy (PDT) elicits a variety of signals that can lead to both cell death and cytoprotection. The irreversible process of apoptosis is readily initiated by mechanisms involving mitochondrial or lysosomal photodamage. An often competing process is autophagy, a pathway that can lead to recycling of photodamaged organelles before they can initiate apoptosis. There can be crosstalk between these processes with sometimes unpredictable results. The net effect is that a relatively minor degree of photodamage can result in a significant level of cell death. More recent studies point to the possibility that combinations of PDT with chemotherapy, or even involving multiple photosensitizers can promote PDT efficacy.