Synergistic intrinsic apoptosis is dependent on the BAX protein. (A) Western blot showing caspase activity with control, single agent, and combo-treated Jeko, Z-138, and Mino MCL cell lines (4 days of exposure). Jeko doses PRT382 at 300 nM, venetoclax at 1 μM, Z-138 doses PRT382 at 150 nM, venetoclax at 10 nM, Mino doses PRT382 at 450 nM, venetoclax at 10 nM. Caspase cleavage was used as an indication of activity, with caspase 8 being indicative of extrinsic apoptosis, caspase 9 of intrinsic apoptosis, and caspase 3 of general apoptosis. (B) Western blots showing the knockdown of BAX and BAK1 proteins after transfection with shRNA against these transcripts in Z-138 and Jeko cells. Values are adjusted by glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and normalized to the empty vector control. (C) Viability of Z-138 and (D) Jeko knockdown variants with control, single agent, or combo treatment for 4 days. Doses as in panel A. At least 3 replicates were completed, and data were measured with annexin V/PI staining and flow cytometry. A 2-way analysis of variance with multiple comparisons was used to determine statistical significance for panels C-D. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001.