Dual inhibition of FOXM1 and its compensatory signaling pathway decreased the survival of ovarian cancer cells.

ABSTRACT

The present study aimed to analyze the compensatory signaling pathways induced by forkhead domain inhibitor­6 (FDI­6), which is a forkhead box protein M1 (FOXM1) inhibitor, in ovarian cancer cells and evaluate the effectiveness of simultaneous inhibition of FOXM1 and the compensatory signaling pathway in decreasing the survival of ovarian cancer cells. The present study identified the proteins involved in the compensatory mechanism activated by FDI­6 in HeyA8 ovarian cancer cells using western blot analysis and a reverse­phase protein array. In addition, a cell viability assay was performed to determine the effects of FDI­6 and the compensatory signaling pathway on cancer cell viability. All experiments were performed in three­dimensional cell cultures. The present study observed that FDI­6 stimulated the upregulation of N­Ras, phosphoprotein kinase Cδ (p­PKCδ) (S664) and HER3 in HeyA8 cells. Tipifarnib as an N­Ras inhibitor, rottlerin as a p­PKCδ (S664) inhibitor and sapitinib as a HER3 inhibitor were selected. The combination of FDI­6 with tipifarnib attenuated the upregulation of N­Ras induced by FDI­6 and the combination of FDI­6 with sapitinib also attenuated HER3 downstream signaling pathway in HeyA8 cells, as shown by on western blot analysis. Rottlerin downregulated p­PKCδ (S664) by inhibiting the activity of a Src­related tyrosine kinase that transfers a phosphate group to PKCδ. Compared with FDI­6 alone, the addition of tipifarnib or rottlerin to FDI­6 was significantly more effective in reducing the growth of HeyA8 cells. However, the combination of FDI­6 and sapitinib did not induce a significant decrease in survival of HeyA8 cells. In conclusion, the addition of tipifarnib or rottlerin to inhibit N­Ras or p­PKCδ (S664), respectively, inhibited the compensatory signaling pathway response induced by FDI­6 in HeyA8 cells. These inhibitors increased the efficacy of FDI­6, which inhibits FOXM1, in reducing ovarian cancer cell viability.