Singlet Oxygen, Photodynamic Therapy, and Mechanisms of Cancer Cell Death

Figure 8

PDT can cause death by the localization of photosensitizer to different organelles. Photosensitizers located in various subcellular location induces cell death through different mechanisms. Normally, photosensitizers are targeted at the plasma membrane, Golgi body, lysosome, endoplasmic reticulum, and mitochondria to cause cell death. Generation of singlet oxygen via photodynamic therapy in the plasma membrane causes cell death through the HOCl signaling pathway (Figure 6) or through disruption of the plasma membrane, which causes cell swelling and rupture (Figure 9(a)). In the Golgi body, singlet oxygen plays a role upstream of mitochondria to cause mitochondria-dependent cell death. Disruption of the lysosome by singlet oxygen causes increased mitochondrial outer membrane permeability (Figure 10(a)), while photodynamic activities in the ER cause misfolding of protein, which triggers unfold protein response (URP), leading to activation of caspase-3 (Figure 10(b)).