Purpose: The cytoprotective mechanism of amifostine (WR-2721) implies free radical scavenging and DNA repair activities. We investigated additional cytoprotective pathways involving intracellular hypoxia and the activation of the hypoxia-inducible factor (HIF) pathway, a key transcription factor regulating glycolysis, angiogenesis and apoptosis, which is also linked with radioresistance.
Materials and methods: The glucose and oxygen levels in the peripheral blood of patients receiving 1000 mg amifostine were determined at various time-points in order to investigate the metabolic changes induced by amifostine. MDA468 breast tumor cell lines were incubated with a high amifostine concentration (10 m M) to overcome the natural resistance of cancer cells to influx of the non-hydrolyzed WR-2721, and the HIF1 alpha protein levels were determined by Western blot analysis. In vivo experiments with Wistar rats were performed in order to assess immunohistochemically changes in the intracellular accumulation of HIF1 alpha induced by amifostine (200 mg/kg).
Results: By 30 min following amifostine administration, the hemoglobin oxygen saturation and pO(2) levels had increased in the peripheral blood while glucose levels had reduced, providing evidence that normal tissue metabolism switches to glycolytic pathways. Incubation of cell lines with amifostine resulted in HIF1 alpha induction. In Wistar rats administration of amifostine resulted in increased HIF1 alpha accumulation in normal tissues.
Conclusions: Since it is doubtful whether dephosphorylation of amifostine to the active metabolite WR-1065 occurs within tumoral tissues (an acidic environment that lacks vascular alkaline phosphatase activity), intracellular hypoxia and upregulation of HIF1 alpha represents an additional, normal tissue-specific, amifostine cytoprotective pathway.