To confirm if MCL1 is the key regulator of RMC-6272-induced apoptosis in breast cancer cells, we overexpressed MCL1 in MCF-7 and ZR-75-1 cells, and observed that MCL1 overexpression was sufficient to rescue cells from RMC-6272-induced cleavage of PARP, as compared with the Luciferase control (Fig. 4B, C). Here, MCL1 is linked to breast cancer.