ONX0912 exerts cytotoxicity on primary WM cells as well as on IgM-secreting low-grade lymphoma cells. Cytotoxicity was assessed by MTT assay in primary WM bone marrow–derived CD19⁺ cells (A; ONX0912 5-250nM; 48 hours); BCWM.1 cells (B; ONX0912 1-500nM; 24-48-72 hours); IgM-secreting low-grade lymphoma cells RL, MEC.1 (C; ONX0912 1-500nM; 48 hours); and freshly isolated primary peripheral blood–derived CD19⁺ cells from 4 healthy donors (D; ONX0912 5-500nM; 48 hours). (E) BCWM.1, RL, and MEC.1 were cultured with ONX0912 (10-100nM) for 2 hours, followed by a 48-hour washout period. Cytotoxicity was assessed by MTT assay at 48 hours. (F) BCWM.1, RL, and MEC.1 were cultured with ONX0912 (10-100nM) for 48 hours and percentage of cells undergoing apoptosis was assessed by DNA fragmentation. (G) BCWM.1 cells were cultured with ONX0912 (2.5-100nM) for 12 hours. Whole-cell lysates were subjected to Western blotting using anti-PARP, –caspase-9, –caspase-3, –caspase-8, –β-catenin, -GRP94, -PERK, –phosphorylated EIF2α (p-EIF2α), -BiP, -PDI, -ATF, and –β-actin antibodies. (H) BCWM.1 cells were cultured with ONX0912 (10-50nM) for 12 and 48 hours. Whole-cell lysates were subjected to Western blotting using anti–phosphorylated EIF2α (p-EIF2α), -BiP, -PDI, and –β-actin antibodies. In all panels, error bars represent SD.