radioprotectants

Radioprotectants are substances that reduce tissue injury caused by ionizing radiation. They are used to protect normal tissues during radiotherapy, to mitigate effects after accidental exposure, or to aid during exposure in space and other high-radiation scenarios. Radioprotectants can be chemical compounds, biological agents, or enzymes that are administered before or after exposure, depending on their mechanism and clinical context.

Mechanisms include scavenging of reactive oxygen species produced by water radiolysis, preservation of cellular redox balance, stabilization of cell membranes, enhancement of DNA repair, and modulation of inflammatory and apoptotic pathways. Many candidates have shown protective effects in preclinical models; only a few have become standard clinical tools.

Amifostine is the best known clinically used radioprotector. It is a prodrug converted to WR-1065, administered intravenously before radiation to reduce xerostomia and nephrotoxicity in certain cancer patients. Other antioxidants, such as N-acetylcysteine, melatonin, selenium, and vitamin E, have been studied, but their clinical utility is limited by mixed efficacy and potential interactions with tumor response.

Limitations include toxicity (e.g., hypotension with amifostine), narrow protective windows, risk of shielding tumor cells, and variable effectiveness across tissues and radiation types. Consequently radioprotectants are used selectively and often as part of risk management rather than general protection.

Emerging approaches focus on targeted delivery, selective protection of normal tissue, and combination strategies to separate protection of healthy tissue from tumor tissue. Research continues in preclinical and early clinical settings, aiming to improve safety, specificity, and applicability in radiotherapy and disaster response.