Pretreatment with the.- secretase inhibitor DAPT sensitizes drug- resistant ovarian cancer cells to cisplatin by downregulation of Notch signaling

Notch signaling is implicated in ovarian cancer tumorigenesis and inhibition of Notch signaling with -secretase inhibitor DAPT resulted in reduction of tumor cell viability and induction of apoptosis in ovarian cancer cells. This study investigated whether DAPT has the same effect on ovarian cancer cells that are resistant to cisplatin and the underlying molecular events. Ovarian cancer cell lines resistant to cisplatin were treated with DAPT, cisplatin or combination for cell viability MTT, flow cytometric cell cycle, ELISA apoptosis and colony formation assays. qRT-PCR and western blotting were used to detect gene expressions. We found that pretreatment of ovarian cancer cisplatin-resistant cell lines with DAPT for 24 h and then with cisplatin for 72 h showed a synergistic antitumor activity in these cell lines, while cisplatin treatment and then addition of DAPT just showed an additive or antagonistic effects on these cisplatin-resistant ovarian cancer cells. Moreover, pretreatment of ovarian cancer cell lines with DAPT and then with cisplatin also inhibited tumor cell colony formation capacity, arrested tumor cells at G2 phase of the cell cycle and induced apoptosis. The cell cycle and apoptosis-related genes, such as cyclin B1, Bcl-2 and caspase-3, were also modulated by the treatment. Pretreatment of ovarian cancer cell lines with DAPT and then with cisplatin downregulated Notch1 and Hes1 expression dose- and time-dependently. The current data demonstrate that DAPT pretreatment was able to sensitize cisplatin-resistant human ovarian cancer cells to cisplatin by downregulation of Notch signaling.