Abstract 5405: Targeting STAT3 as a novel therapy for ovarian clear cell carcinoma

Abstract

Abstract Objective: Advanced ovarian clear cell carcinoma (OCCC) carries a very poor prognosis in large part secondary to the high rate of resistance to standard platinum and taxane chemotherapy. STAT3 expression and activation has been shown to regulate tumor progression in various human cancers though has not been well studied in OCCC. Preliminary work in our lab has demonstrated constitutive activation of STAT3 (pSTAT3Tyr705 or pSTAT3727) in OCCC cell lines as well as human OCCC tumor tissue samples. Significantly, pSTAT3 is expressed in the absence of other forms of activated STAT (pSTAT1,2,6). Based on our preliminary data, we hypothesized that use of a novel STAT3 inhibitor, HO-3867, would be an effective agent against OCCC cell lines in vitro and in vivo using a novel orthotopic mouse model. Methods: Five OCCC cell lines (JHOC, OVISE, OVTOKO, RMGV, and ES2) were treated with HO-3867, cisplatin, or paclitaxel alone and/or in combination. Protein expression in tumor tissue and cell lines was determined by western blot (WB) and RT PCR was used to analyze RNA expression levels. MTT assay, BrdU assay, ANNEXIN V kit and flow cytometry were used to analyze cell viability, proliferation, apoptosis and cell cycle arrest. We use a novel orthotopic murine model using an ovarian bursal injection which was developed in our laboratory and has demonstrated primary ovarian tumor development and peritoneal carcinomatosis. Results: Treatment with HO-3867 decreased expression of pSTAT3 while total STAT3 remained constant. Treatment with cisplatin or paclitaxel resulted in a relative increase in pSTAT3. The inhibitory effect of HO-3867 on cell proliferation is associated with G2/M phase cell cycle arrest and apoptosis (>45%) within 24 hours of treatment. Treatment with HO-3867 resulted in a decrease in BCL2 and cleavage of caspase 3, caspase 7, and PARP confirming induction of apoptosis after treatment with HO-3867. Treatment with cisplatin or paclitaxel was less effective at decreasing cell viability, reducing proliferation, and inducing apoptosis. In vivo experiments using the orthotopic murine model are ongoing. Conclusion: HO-3867, a novel STAT3 inhibitor, appears to be efficacious against OCCC in vitro as compared to standard chemotherapeutics. Further investigation into this novel therapy is warranted given the generally poor response of OCCC to our standard chemotherapy regimens. Experiments to investigate the efficacy of HO-3867 in OCCC in vivo are underway. Citation Format: Kristin L. Bixel, Uksha Saini, Jack Fowler, Sneja Rajendran, Ross Wanner, Noriomi Matsumura, Kalman Hideg, Ikuo Konishi, David Cohn, Selvendiran Karrupaiyah. Targeting STAT3 as a novel therapy for ovarian clear cell carcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5405. doi:10.1158/1538-7445.AM2015-5405