amifostine

Amifostine is an organic thiophosphate cytoprotective agent known chemically as 2-[(3¬ aminopropyl)amino]ethanethiol dihydrogen phosphate (ester), it’s adjuvant used in cancer chemotherapy and radiotherapy involving DNA-binding chemotherapeutic agents. It is marketed under the trade name Ethyol. Amifostine is a prodrug and is dephosphorylated by alkaline phosphatase in tissues to a pharmacologically active free thiol metabolite. This metabolite is believed to be responsible for the reduction of the cumulative renal toxicity of cisplatin and for the reduction of the toxic effects of radiation on normal oral tissues. The ability of Ethyol to differentially protect normal tissues is attributed to the higher capillary alkaline phosphatase activity, higher pH and better vascularity of normal tissues relative to tumor tissue, which results in a more rapid generation of the active thiol metabolite as well as a higher rate constant for uptake into cells. The higher concentration of the thiol metabolite in normal tissues is available to bind to, and thereby detoxify, reactive metabolites of cisplatin. This thiol metabolite can also scavenge reactive oxygen species generated by exposure to either cisplatin or radiation. Healthy cells are preferentially protected because amifostine and metabolites are present in healthy cells at 100-fold greater concentrations than in tumor cells. — NCATS