(A) Combined caspase-3 and caspase-7 activity in SH-SY5Y, SMS-KCNR, LAN-5 and CLB-GA cells after treatment with 125 nM or 250 nM of idasanutlin and/or venetoclax for 24 hours relative to vehicle-treated control cells. Caspase-3/7 activity was higher when cells were treated with venetoclax and idasanutlin as compared to each compound alone. Columns represent the average of two different experiments, each done in duplicate. Caspase-3/7 activity of the idasanutlin-venetoclax combination was compared to idasanutlin and venetoclax alone using the Mann–Whitney test. *p < 0.05. Error bars represent the standard deviation. (B) Immunoblot analysis of PARP cleavage in SH-SY5Y, SMS-KCNR, LAN-5 and CLB-GA cells after treatment with either 62.5 nM (+), 125 nM (++), or 250 nM (+++) of idasanutlin and/or venetoclax for 24 hours. Cleavage of PARP, a hallmark of apoptosis, was evident after combined idasanutlin / venetoclax treatment in all four cell lines. Vinculin was used as a loading control.