Amifostine : The preclinical basis for broad-spectrum selective cytoprotection of normal tissues from cytotoxic therapies

: Administered prior to cytotoxic chemotherapy or radiation, the aminothiol amifostine provides broad-spectrum cytoprotection of various normal tissues without attenuating antitumor response. The basis for the selectivity of action resides in the anabolism of amifostine at the normal tissue site by membrane-bound alkaline phosphatase. Dephosphorylation to the free thiol WR-1065 is followed by rapid uptake into normal tissues by a carrier-mediated facilitated diffusion process. In contrast, uptake into tumor tissues is slow to negligible. Pretreatment with amifostine provides protection of normal tissues from the cytotoxic effects of alkylating agents, organoplatinums, anthracyclines, taxanes, and radiation. Additionally, the mutagenic and carcinogenic effects of these modalities are also attenuated. Preclinical studies show significant protection of marrow progenitor cells that give rise to the red blood cells, white blood cells, and platelets. Protection of kidneys and neural tissues from cisplatin toxicity has been shown, along with protection of the heart, intestinal crypt cells, and pulmonary tissues from chemotherapy and radiation, as well as vasculoconnective and musculoconnective tissue in an irradiated field. Comparative in vitro and in vivo studies using murine and human tumor xenografts show no attenuation of antitumor effects of these same therapies despite the protection of normal organs. The unique preclinical profile of amifostine serves as the basis for the clinical development program for this important new broad-spectrum cytoprotective agent.