Positive correlation between MDM2 levels and apoptosis and effect of MDM2 inhibitor on AML progenitors in primary AML samples. (A) Correlation of MDM2 protein levels relative to normal bone marrow cells with degree of apoptosis by MDM2 inhibition in 16 primary AML cells with wild-type p53. MDM2 protein expression levels relative to an internal control, β-actin, were determined in each sample, and then compared with normal bone marrow cells. There was a significant positive correlation between relative MDM2 levels and the percentage of specific annexin V induction (r = 0.805, P < .01). (B) Effect of Nutlin-3a on AML and normal clonogenic progenitors. Data represent average results from 5 different AML samples (white bar) and 5 magnetically separated normal CD34⁺ cells (gray bars). Results are expressed as the mean plus or minus the standard error of the mean (SEM) of the number of colonies in the presence of 1 μM Nutlin-3a compared with the number in control cells. *P < .05.