Signal Transducers and Activators of Transcription 3 Pathway Activation in Drug-Resistant Ovarian Cancer

Abstract

Purpose: One of the major obstacles in the treatment of ovarian cancer is the development of multidrug resistance. Recent evidence shows that high-grade ovarian cancer often shows activation of the signal transducers and activators of transcription 3 (Stat3) pathway with subsequent transcription of genes that support tumor growth and survival. Less studied is the role of the Stat3 pathway in acquired drug resistance. There is no information on Stat3 expression in chemotherapy naI« ve ovarian cancer as compared with tumors collected later in the natural history of the disease. To further clarify the significance of Stat3 activation in ovarian cancer, here we investigated the Stat3 expression and activation in ovarian cancer and ovarian cancer multidrug resistance cell lines. Experimental Design: Western blotting, electrophoretic mobility shift assay, luciferase assays, ELISA assay, and real-time reverse transcription-PCR determined interleukin-6 and Stat3 pathway expression and activation in cell lines. Stat3 expression in ovarian cancer tissue microarray was evaluated by immunohistochemistry. Results: Activated (phosphorylated) Stat3 is overexpressed in most paclitaxel-resistant ovarian cancer cells. Inhibition of Stat3 activation results in significant decreases in paclitaxel resistance and enhanced apoptosis. Drug-resistant recurrent tumors have significantly greater phosphorylated Stat3 (pStat3) expression as compared with matched primary tumors. Tumors with associated inflammatory cell infiltrates also have a higher proportion of cells staining intensely for nuclear phosphorylated Stat3 as compared with tumors without inflammatory infiltrates, consistent with paracrine activation of the Stat3 pathway by immune-mediated cytokines. Conclusions: These data support the hypothesis that interruption of Stat3 signaling could reverse resistance to paclitaxel and perhaps other chemotherapy agents in human cancer.

CDDO-Me, a synthetic triterpenoid, inhibits expression of IL-6 and Stat3 phosphorylation in multi-drug resistant ovarian cancer cells

“…Previously, we have found that IL-6 is secreted in high levels by several paclitaxel-resistant ovarian cancer cell lines, including SKOV-3 TR and OVCAR8 TR [7,8]. SKOV-3 TR and OVCAR8 TR cells were plated at 1×10 5 cells per well in 24-well plates and treated with CDDOMe in both a time-and dose-dependent manner.…”

“…SKOV-3 TR and OVCAR8 TR cells were plated at 1×10 5 cells per well in 24-well plates and treated with CDDOMe in both a time-and dose-dependent manner. The supernatants were collected at different time points and kept at −20° C. IL-6 levels in culture supernatants were measured using a quantitative ELISA kit (R&D Systems, Minneapolis, MN) as described previously [7,8]. The absorbance of each well was read using a BT 2000 Microkinetics Reader (Bio-Tek Instrument Inc. Winooski, VT) at 450 nm.…”

“…There is no therapy to overcome drug resistance in ovarian cancer. The development of chemoresistance is associated with many events, such as defective apoptotic signaling in response to drugs, overexpression of antiapoptotic proteins such interleukin 6 (IL-6), Bcl-2, BcL-X L , or survivin, and overexpression of multidrug resistance (MDR) gene protein pgp1 [6][7][8][9]12]. Successful management of ovarian cancer would be greatly aided by novel agents that interfere with both intrinsic and acquired mechanisms of drug resistance mechanisms.…”

“…IL-6 is a progrowth, proangiogenic and anti-apoptotic cytokine that has been elevated in serum and ascites of patient with ovarian cancer as well as in culture supernatant of multi-drug resistant cell lines [8,[19][20][21]. In many tumors, elevated IL-6 levels in the serum is predictive of poor clinical outcome.…”

“…We have previously shown that progressive paclitaxel resistance in vitro is associated with increasing IL-6 expression in ovarian cancer cell lines and showed that transfection of IL-6 (a Stat3 activating ligand) into some cell lines induced paclitaxel resistance [7,10]. Recently, several studies have demonstrated that Stat3 is highly activated in high-grade as well as recurrent drug resistant ovarian cancer tumor cells [8,18,22,25]. Constitutive activation of the Stat3 pathway has been shown to confer resistance to chemotherapy-induced apoptosis in epithelial malignancies [2].…”