Elevating the Reactive Oxygen Species in Cancer Cells by Photodynamic Therapy: Pro-oxidative Approach for Cancer Treatment

Photodynamic therapy (PDT) is a treatment administered to patients by using photosensitizing agents. PDT systems work by combining the effect of light, photosensitizer (PS) dye, and oxygen. PDT can target cancer tissue when PS specifically localizes to the tumor cells, then with a laser, it activates by inducing a photochemical reaction which in turn can eradicate the abnormal cells and cure various types of cancer. The reactive oxygen species (ROS) initiated in the mitochondria leads to cell death, where it takes up an exogenous PS on its own. Endogenously assembled photosensitizer has been shown to cause direct tumor cell death through necrosis, apoptosis, autophagy, and vascular destruction. ROS generated by PDT also activate the immune system by minimally affecting the surrounding tissue. As a result, PDT-mediated cell death is correlated with inhibition of tumor growth. This chapter summarizes the use of natural and artificial PS compounds in different cancers, their cell death pathway mechanism, and future perspectives of PDT.