Photodynamic therapy regulates fate of cancer stem cells through reactive oxygen species

Figure 1 The process of reactive oxygen species production and transformation in cancer stem cells. A: The photosensitizer is activated from the ground singlet state to the excited singlet state and triplet state. The excited singlet state and triplet state can release energy through fluorescence and phosphorescence, or transfer energy to generate various reactive oxygen species (ROS); B: The mutual transformation of ROS in vivo. These ROS all affect the self-renewal, sphere formation, invasion, and apoptosis of cancer stem cells. PS: Photosensitizer; H₂O₂: Hydrogen peroxide; SOD: Superoxide dismutase; •OH: Hydroxyl radicals; OH⁻: Hydroxyl; NO: Nitric oxide; ONOO⁻: Peroxynitrite anion; NO₂: Nitrogen dioxide.