Subcellular targets for photodynamic therapy: implications for initiation of apoptosis and autophagy.

Direct lethal effects of photodynamic therapy (PDT) on a cell population were initially shown to occur via initiation of apoptosis, with high doses having a necrotic effect. Selective induction of cellular "self-digestion," better known as autophagy, represents a novel therapeutic target for the prevention of tumor growth and metastasis. It should be noted that autophagy has conflicting roles in the regulation of cell death, which, when applied to oncology, may produce both positive and negative effects on tumor development. Through better understanding the complex parts played by autophagy among diverse cellular signaling pathways in preclinical models, it may be possible to selectively regulate autophagy in response to specific stimuli, thereby inhibiting its oncogenic tendencies while preserving its tumor-suppressive capabilities.