Amifostine: the first selective-target and broad-spectrum radioprotector.

After several decades of preclinical and clinical research, the first approved radioprotective drug, amifostine, is being used in clinical practice. Amifostine has been shown to specifically protect normal tissues from damage caused by radiation and chemotherapy. An inactive prodrug, amifostine is converted to an active thiol by dephosphorylation by alkaline phosphatase in the normal endothelium. The hypovascularity and acidity of the tumor environment and the differential expression of alkaline phosphatase in normal and neoplastic tissues contribute to its cytoprotective selectivity. The cytoprotective mechanism of amifostine is complicated, involving free-radical scavenging, DNA protection and repair acceleration, and induction of cellular hypoxia. The U.S. Food and Drug Administration has approved the i.v. use of amifostine to reduce the cumulative renal toxicity associated with repeated administration of cisplatin in patients with advanced ovarian cancer and to reduce the incidence of moderate to severe xerostomia in patients undergoing postoperative radiation treatment for head and neck cancer, where the radiation port includes a substantial portion of the parotid glands. Nonetheless, amifostine has potential applications in many other oncologic settings. Novel schedules and routes of administration are under investigation and may further simplify the use of amifostine, reduce any undesired effects, and considerably broaden its applications. This review summarizes the clinical experience with amifostine and provides insight into future clinical directions.