Simultaneous assessment of p53 and MDM2 expression in leukemic cells in response to initial prednisone therapy in children with acute lymphoblastic leukemia.

Ineffective apoptosis is one of main causes of a treatment failure in childhood acute lymphoblastic leukemia (ALL). p53 plays a crucial role in triggering apoptosis of ALL in response to prednisone treatment. MDM2 is the endogenous inhibitor of apoptosis that downregulates the functional activity of p53 protein. This study is aimed to evaluate changes in MDM2 and p53 expression in peripheral blood mononuclear cells collected from children with ALL prior to and after 6 and 12 h of prednisone administration in relation to early treatment response. The study comprised 35 children with newly diagnosed ALL, subdivided into good (n = 24) and poor (n = 11) early treatment responders. MDM2 - associated APC fluorescence and p53 - associated FITC fluorescence were measured by the laser scanning cytometer. In the group of poor responders, p53 and MDM2 fluorescence were significantly higher than in the group of good responders. In the group of good early treatment responders, a statistically significant rise of p53 fluorescence measured in the nucleus and in the cytoplasm 12 h after prednisone administration as well as increase in MDM2 fluorescence measured in the cytoplasm 6 and 12 h after prednisone administration were seen. These data suggest that pretreatment overexpression of MDM2 protein may contribute to poor early treatment response.