Effects of low-dose cytarabine on the viability and proliferation of primary human AML cells. (A) The viability of primary human AML cells after 40 hours of in vitro culture in medium alone. Cytarabine seems to have a dose-dependent toxic effect, but the difference reached statistical significance only for the two highest drug concentrations (0.5 and 0.05 μM). (B) Low-dose cytarabine showed a dose-dependent antiproliferative effect for the leukemic cells when testing cytokine-dependent AML cell proliferation (medium supplemented with 20 ng/mL of GM-CSF, SCF and Flt3l). The growth inhibition reached statistical significance even when testing cytarabine 0.01 μM. All results are presented as the mean with SD, the pair sample t-test was used for the statistical analyses of the apoptosis data, and the Wilcoxon signed rank test for the proliferation data (*p <0.05; **p <0.01; ***p <0.001).