NPI-0052 induces decrease in DNA synthesis, triggers cytotoxicity, and induces apoptosis in WM cells. (A) Thymidine uptake assay and cytotoxicity assessed by MTT. BCWM.1 cells were cultured with NPI-0052 (2.5-40 nM) for 48 hours. (B) Thymidine uptake assay. Several IgM-secreting cell lines, WM-WSU (♦), MEC-1 (■), and Namalwa, were cultured with NPI-0052 (2.5-40 nM) for 48 hours. (C) Several IgM-secreting cell lines, WM-WSU, MEC-1, and RL, were cultured with NPI-0052 for 48 hours. Cytotoxicity was assessed by MTT assay. (D) Freshly isolated bone marrow CD19⁺ tumor cells from 4 patients with WM were cultured with NPI-0052 (2.5-40 nM) for 48 hours. Cytotoxicity was assessed by MTT assay. (E) Freshly isolated PBMCs from 4 healthy donors were cultured with NPI-0052 (2.5-40 nM) for 48 hours. Cytotoxicity was assessed by MTT assay. (F) BCWM.1 cells were cultured with NPI-0052 for 48 hours at doses that range from 2 to 30 nM, and the percentage of cells undergoing apoptosis was studied by Apo2.7 staining. (G) BCWM.1 cells were cultured with NPI-0052 (2.5-20 nM) for 12 hours. Whole-cell lysates were subjected to Western blotting using anti–caspase-8, -PARP, –Mcl-1, -Smac/DIABLO, -cIAP1, -XIAP, -survivin, and –α-tubulin antibodies.