Copper-Cysteamine Nanoparticles As New Radio/Photosensitizer With Low Sunlight Toxicity*

Photodynamic therapy is a new cancer treatment modality that uses singlet oxygen and other reactive oxygen species to kill cancerous cells. However, most conventional photosensitizers are toxic to not only cancerous cells but also to normal cells. Most of these PSs can be excited by UV-Vis light and therefore results in unwanted toxicity under sunlight and bright room light exposure. Therefore, PDT treated patients are required to avoid bright light for up to six weeks. Copper cysteamine(Cu-Cy) nanoparticle, which was invented by our group in 2014, is a new type of photosensitizer and a novel radiosensitizer that can be activated by X-ray, UV-light, microwave, and ultrasound to produce singlet oxygen and other types of reactive oxygen species for cancer treatment. The Cu-Cy nanoparticle has strong absorption in UV-region but not in the visible region and hence may not produce ROS under sunlight. In the present article, we report comparative toxicity study of Cu-Cy and PPIX (an FDA approved PSs) and show that while Cu-Cy is toxic to cancer cells, it is highly safer to normal cells. On the other hand, PPIX is toxic to both cancer and normal cells.