A–D) U937_vec and U937_EVI1 cells were treated with the indicated concentrations of etoposide (A, C) or daunorubicin (B, D) for 48 h. Cellular viability/metabolic activity was determined based on ATP content (A, B), and apoptosis was measured via caspase 3/7 activity (C, D). Data points represent the mean +/− SEM from at least three independent experiments. *, p<0.05 (paired Student’s t-test). E) Nuclear morphology of U937_vec and U937_EVI1 cells after treatment with or without 400 nM etoposide for 48 h. Apoptotic nuclei are marked by arrows. Please note difference in scale between etoposide and control treated cells. F) Quantitative assessment of nuclear morphology. Nuclei prepared as in E were counted as ‘intact’ or ‘apoptotic’ (see Methods) by an observer blinded to the identity of the samples. Data points represent the mean+SEM from 3 independent experiments. **, p<0.01; n.s., not significant (paired Student’s t-test).