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

Figure 5

Process of ROS generation in a cancer cell due to photodynamic treatment. Photosensitizer (PS) specially designed for a particular cancer cell receptor will bind with it through the cancer target ligand. After recognizing the photosensitizer, the cancer cell takes it up through receptor-mediated endocytosis. The cellular environment inside the cancer cell is different from the extracellular space. The protease enzyme in the cell activates the engulfed PS by cleaving the quencher, and when the light is focused on the activated PS, it gets excited and converts the oxygen to ROS. ROS, such as singlet oxygen, causes cell death through several mechanisms. Sometimes, the sensitizer may be activated in the extracellular space due to acidity and hypoxia.