PLK1 and breast cancer: As the inhibition of WEE1 G2 checkpoint kinase (WEE1), a downstream PLK1 protein that is important for mitosis progression, and ATR is effective in breast cancer and other cell lines63, the combination of AZD-6738, an ATR inhibitor, and NMS-P937, a PLK1 inhibitor, was effective and synergistic in MIAPaCa-2 (Fig. 7c).