Figure 2. Cytotoxicity profiles of NNU219 and bortezomib against tumor cell lines, primary myeloma cells and human PBMC. (A, B) Hematological and solid tumor cell lines were treated with NNU219 and bortezomib. Cell viability was measured with CCK8 reagent either after 1 h of compound treatment followed by 72 h washout period (A) or continuous compound treatment for 72 h (B). The IC50 value as a measure the cytotoxic effects of tested compounds. Values were the mean ± SD from 3 determinations (**, p < 0.01; ***, p < 0.001). (C) Purified patient MM cells (CD138+) were treated with increasing concentrations of NNU219. The cytotoxic effects of NNU219 were determined by bioluminescent measurement of cellular ATP using Cell Titer-Glo reagent after 24 h treatment. Results were expressed as % cell viability over DMSO control. Data were presented as mean ± SD of triplicate samples (p < 0.001 for all patient samples). (D) CD138+ cells from MM patient no. 4 (newly diagnosed) and no. 5 (refractory) were treated with NNU219 for 36 h and 48 h, respectively. Data were presented as mean ± SD of triplicate samples (p < 0.001). (E) CD138- cells from MM patient no. 4 and no. 5 were treated with NNU219 for 24 h. Data were shown as mean ± SD of triplicate samples. (F) PBMCs from healthy volunteers were treated with increasing concentrations of NNU219 and then analyzed for viability using Cell Titer-Glo assay. Data were shown as mean ± SD of triplicate samples.