Abrogation of constitutive Stat3 activity circumvents cisplatin resistant ovarian cancer.

The aim of the present study was to investigate the role of Stat3 in cisplatin resistant ovarian cancer. It was first demonstrated that higher activated Stat3 was detected in cisplatin-resistant ovarian cancer cell lines. To provide evidence that supported the hypothesis that phosphorylated-Stat3 expression may promote cisplatin resistance, ectopic Stat3 was expressed by IL-6 stimulation that partially abrogates Stat3, as opposed to the knock-down of Stat3 by specific siRNA that restores cisplatin sensitivity against ovarian cancer cells. This hypothesis was further confirmed by clinical tumor specimens of ovarian cancer obtained from patients with cisplatin-resistance. Based on these premises, Stattic, an effective small molecular inhibitor of Stat3, was used to inhibit Stat3 activation. The data presented here show that Stattic restored the sensitivity to cisplatin in chemoresistant ovarian cancer by significant reductions in the expression of the anti-apoptosis protein Bcl-2, Bcl-XL, Survivin protein and phosphorylated-Akt levels. Consistent with these observations, this experiment demonstrated the first evidence of Stattic circumvented cisplatin resistance of orthotopic xenograft ovarian cancer in vivo. Altogether, these findings emphasize the importance of Stat3 in cisplatin resistance in ovarian cancer and provide a further impetus to clinically evaluate biological modifiers that may circumvent cisplatin resistance in patients with chemoresistant ovarian cancer.