Activatable Photodynamic Photosensitizers for Cancer Treatment

Photodynamic therapy (PDT) is a clinically approved treatment modality used for a wide range of medical conditions, including malignant cancers. It employs cytotoxic reactive oxygen species (ROS), particularly singlet oxygen (1O2), to kill cells of interest and has attracted immense attention during the last decades. Molecular design of triplet photosensitizers is no doubt at the core of successful PDT action. Spatiotemporal control of ROS generation and consequent cancer cell selectivity is one of the highly sought characteristics of new-generation photosensitizers, to minimize severe adverse effects as well as to enhance the therapeutic outcome. Activatable photosensitizers have appeared to be a good candidate in this respect as they tend to stay in their “off” state prior to activation with various tumor-associated intracellular stimuli. In this chapter, we summarize the recent advances in the field of activatable photosensitizers by focusing on the design principles and biologically relevant activators.