XIAP inhibitor induces apoptosis in primary AML samples. (A) Primary AML blasts were isolated from peripheral blood samples obtained from patients with AML who had more than 80% blasts in the peripheral blood. As a control, mononuclear cells were isolated from samples of normal mobilized peripheral blood cells or from bone marrow. Primary blasts or normal hematopoietic mononuclear cells were treated with increasing concentrations of the XIAP inhibitor antagonist 1396-12 for 24 hours. After treatment, apoptosis was measured by annexin V surface expression. For each sample, the percentage of apoptosis after treatment with 10 μM of 1396-12 is shown with the LD₅₀ displayed along the x-axis. (B) XIAP inhibitor is equally effective in samples from patients with chemosensitive and chemoresistant AML. The LD₅₀ for 1396-12 is compared between samples derived from patients who achieved complete remission with induction chemotherapy (CR), had no response to induction chemotherapy (NR), or who were in relapse. The horizontal line represents the median LD₅₀ for the group. (C) Colony formation assay. Primary AML blasts (—) or mobilized normal peripheral blood stem cells (-) were treated with increasing concentrations of the XIAP antagonist 1396-12 or buffer control for 24 hours. After treatment, cells were washed, plated in methylcellulose cultures, and counted after one week. For each sample, the mean plus or minus SD of 3 experiments expressed as a percentage of the buffer treated control is shown. Each symbol represents an individual patient.