The cytoprotective aminothiol WR1065 activates p21waf-1 and down regulates cell cycle progression through a p53-dependent pathway.

The phosphoaminothiol WR1065, the active metabolite of the pro-drug amifostine (WR2721), protects cultured cells and tissues against cytotoxic exposure to radiation or chemotherapeutic agents. We show here that WR1065 and the pro-drug WR2721 activate the p53 tumor suppressor protein and induce the expression of the cyclin-dependent kinase inhibitor p21waf-1 in the breast cancer cell line MCF-7, and in the mouse fibroblast cell line balb/c 3T3. Using two MCF-7 derived cell lines, MN1 and MDD2, we show that induction of p21waf-1 is detectable in MN1 (expressing a functional p53) but not in MDD2 (p53 disabled). These effects are observed at concentrations of WR1065 (0.5 to 1 mM) identical to those required to protect against cytotoxicity by hydrogen peroxide. Induction of p53 is not prevented by addition of aminoguanidine, an inhibitor of Cu-dependent amine-oxidases which blocks the extra-cellular degradation of WR1065 into toxic metabolites. Moreover, spermidine, a natural polyamine structurally related to amifostine, does not activate p53. Induction of p53 by WR1065 results in a delay in the G1/S transition in MCF-7 and MN-1 cells, but not in the p53 disabled cells MDD2. These data indicate that WR1065, a polyamine analog with thiol anti-oxidant properties, activates a cell cycle check-point involving p53.