Radioprotectors, Radiomitigators, and Radiosensitizers

Abstract This chapter gives an overview of molecules and mechanisms able to intervene with the biological effects of ionizing radiation (IR), either related to their clinical use in radiotherapy or in the field of radiation protection in case of an accidental exposure to radiation and/or nuclear emergencies. According to the National Cancer Institute, “radiomodifiers” can be classified into (a) radioprotectors (protect molecules and tissues from direct and indirect damage induced by IR) or (b) radiomitigators (reduce and help to repair damage), depending on whether they are administered pre- or post-IR exposure, respectively. Most of them are free radical scavengers and antioxidants (or enhancers of the antioxidant defenses), increase DNA repair mechanisms, have anti-inflammatory properties, and/or prevent cell death. On the other hand, (c) radiosensitizers directly or indirectly enhance DNA damage and ROS production, increasing IR toxicity on tumor cells, thus they are used to increase radiotherapy efficacy in cancer patients. The section “Radionuclides and methods to treat contaminated individuals” describes the medical consequences and treatment modalities of internal contamination by radionuclides. Overall, the chapter discusses the effects of most currently known radiomodifiers, their specific properties, and their mechanisms of action, by emphasizing results obtained in recent preclinical and clinical trials.