NOTCH1 and ovarian cancer: To further investigate the functional role of Notch1 signaling in the chemoresistance of ovarian cancer, a γ-secretase inhibitor (GSI XXI, compound E, 10 μM) was used to inhibit Notch1 activity in the chemoresistant ovarian cancer cells A2780cp, C13*, SKOV3 and ES-2 (Fig. 6B).