CDKN1A and breast cancer: Furthermore, similar results were also obtained in the metastatic breast cancer cell line MDA-MB-231 depleted of endogenous p21 with siRNA #2 and treated with Poloxin for 24 h, which displayed an increase in caspase-3/7 activities (Fig. 5G) and in cleaved PARP compared to control cells (Fig. 5H, 1st panel and ratio).