Effects of Plk1 inhibition on normal hematopoietic CD34⁺ progenitors and AML primary cells from patients. (A) Fresh AML cells were grown in clonogenic assays in the presence of increasing doses of BI2536. Results are presented as percentage of control and are mean ± SD of duplicates from 5 patients tested. (B) AML cells from patients were transfected with Plk1-specific or control siRNA, and grown in clonogenic assays as in panel A (top panel). Representative data showing the efficiency of PLK1 knockdown by Western blot are shown (bottom panel). Results are presented as percentage of control for each patient, and the absolute number of colonies for each control condition was indicated on the top of the figure. (C) Normal CD34⁺ progenitors were grown for 14 days in similar conditions as in (A), in the medium indicated in “Methods.” Results shown are mean ± SD of 2 independent experiments performed in duplicate. (D) Primary AML cells were grown in liquid cultures in the conditions described in “Methods,” and counted each day in the presence of trypan blue. The proliferation rate was compared in the presence of 1 nM and 10 nM, or in the absence of B12536. This experiment is representative of results obtained with 4 patients. (E) Same experiment as in panel C, but performed with primary normal CD34⁺ cells from healthy donors. This graph is representative of 2 experiments performed in duplicate.