Pracinostat shows preferential cytotoxicity toward BCR-DLBCLs. (A) BCR-DLBCLs (green bars; n = 7) and OxPhos-DLBCLs (red bars; n = 4) were treated with 250 nM pracinostat for 72 hours before staining with annexin V (AnnV) and 7-aminoactinomycin D (7-AAD) for apoptosis analysis by fluorescence-activated cell sorting (FACS). The upper part of each bar represents the percentages of apoptotic, annexin V–positive cells (AnnV+), and the lower part represents the percentage of nonapoptotic, 7-AAD–negative/annexin V–negative (7-AAD–/AnnV–) cells. A subset of BCR-DLBCLs showed marked apoptosis induction after pracinostat treatment (4 of 7); for OxPhos-DLBCLs, the percentage of apoptotic cells was negligible. (B) Cells were treated with pracinostat as above in panel A, then fixed and stained with 7-AAD before cell cycle analysis by FACS. In agreement with the apoptosis assay, BCR-DLBCLs frequently showed marked accumulation in sub-G₁. Conversely, OxPhos-DLBCLs were characterized by G₁ arrest and minor sub-G₁ accumulation. Top: BCR-DLBCLs; bottom: OxPhos-DLBCLs. (C) Cells were treated with 250 nM pracinostat or DMSO for 14 days, with cell count, medium change, and drug replenishment every 3 to 4 days. For each data point, the number of live cells for pracinostat was normalized to the number of live DMSO-treated cells. (D) BCR-DLBCLs and OxPhos-DLBCLs were treated with 250 nM pracinostat for 14 days before processing for cell cycle analysis by FACS. Experiments were performed at least twice. Error bars denote the standard error of the mean (SEM). Two-sided Student t test: *P < .05; **P < .01; ***P < .001.