STAT3 Inhibitor Napabucasin Inhibits Tumor Growth and Cooperates with Proteasome Inhibition in Human Ovarian Cancer Cells.

BACKGROUND Ovarian cancer is a disease with the highest mortality in gynecologic malignancies. Activation of STAT3 pathway is well known to be associated with tumor progression and metastasis in a number of cancers including ovarian cancer. Therefore, STAT3 may be an ideal target for ovarian cancer treatment. OBJECTIVE The present study aims to determine the antitumor activity of STAT3 inhibitor Napabucasin as a single agent or in combination with proteasome inhibitor MG-132 in ovarian cancer cells. METHODS MTT was performed to determine the anti-proliferative effect of Napabucasin on ovarian cancer SKOV-3 cells. The involved anti-tumor mechanism was explored by flow cytometry, qRT-PCR and western blot. MDC staining and tandem mRFP-GFP-LC3 fluorescence microscopy were used to analyze the autophagy inducing capability of Napabucasin with or without MG-132. The combinational anticancer effect of Napabucasin and MG-132 was evaluated according to Chou and Talalay's method (1984). RESULTS Napabucasin showed obvious tumor-inhibitory effects against SKOV-3 cells. Treatment by Napabucasin arrested cell cycle progression in G2/M phase. Mechanistically, elevated expression of p21 may contribute to the blockade of cell cycle. Moreover, we demonstrated that Napabucasin induced autophagy in SKOV-3 cells by using various assays including MDC staining, autophagic flux examination, and detection of the autophagy markers. In addition, combination of Napabucaisin with MG-132 exhibited significant synergistic anti-proliferative effect, probably by inducing apoptosis through a mitochondria-dependent pathway. The two compounds induced pro-survival autophagies, and co-treated with autophagy inhibiter might further enhance their antitumor effects. CONCLUSION Napabucasin alone or in combination with MG-132 might be promising treatment strategies for ovarian cancer patients.