Abstract 2517: STAT3 inhibition by LLL12 in combination with niclosamide and chemotherapy in ovarian cancer

Objective: Chemoresistance and recurrence invariably develop in the treatment of ovarian cancer, despite initial response to chemotherapy. Recent studies have shown that signal transducer and activator of transcription-3 (STAT3) signaling is associated with recurrence and development of chemoresistance in ovarian cancer. A novel small molecule, LLL12, has been shown to inhibit STAT3 in many solid tumors including colon, breast, and glioma. Niclosamide, an FDA approved salicyclamide derivative used for the treatment of tapeworm infections, has also been shown to inhibit STAT3 and other pathways including mTOR, Wnt, NfkB. Therefore, the objective of this study was to investigate LLL12 alone and in combination with niclosamide and/or chemotherapy as a potential treatment for ovarian cancer. Methods: Ovarian cancer cell lines A2780 and SKOV3ip2 and their carboplatin and paclitaxel chemoresistant derivatives A2780.cp20, SKOV3ip2.TR were initially treated with LLL12 alone (0.1 nM - 10 µM). These cell lines were treated with the IC50 values for LLL12 alone in combination with niclosamide (0.1 - 5 µM). Ascites was collected from a patient undergoing surgery for ovarian cancer and treated concurrently with LLL12 (0.5 - 10 μM) and carboplatin (25 - 100 μM). Cell viability was assessed using the ATP-lite assay. All samples were assayed in quadruplicate and reported as the mean ± SE. Results: Combination treatment with LLL12 and niclosamide produced increased cytotoxicity compared to LLL12 alone in all ovarian cancer cell lines. Treatment with chemotherapy and LLL12 showed additive cytotoxicity in the patient-derived tumorspheres. The IC50 dose of LLL12 against A2780 cells was 0.2 ± .06 but when this dose was combined with 1 µM of niclosamide, 100% cytotoxicity was achieved; 1 µM of niclosamide alone produced 80% cytotoxicity. With the A2780.cp20 cell line, LLL12 had an IC50 of 0.79 ± µM, but with 1 µM of niclosamide there was 100% cell kill, and 80% with niclosamide alone. Both SKOV3 and SKOV3ip2.TR cell lines had higher IC50 values for LLL12 (4.25 µM ± 2.1 and 2.29 µM ± 1.4, respectively) and an additive effect was achieved in both cell lines when LLL12 was combined with niclosamide. In the patient sample, a dose of 50 µM of carboplatin alone killed 10% of cells, and 10 µM of LLL12 killed 50%, The combination of 10 µM of LLL12 and 50 µM of carboplatin killed 80% of the cells; therefore an additive cytotoxicity was seen with carboplatin and LLL12. Conclusion: This study demonstrates that the STAT3 inhibitor, LLL12, is active against ovarian cancer cell lines and tumorspheres from a patient sample. Future animal xenograft studies will elucidate more about its activity in combination with other agents such as niclosamide and chemotherapy. Citation Format: Rebecca C. Arend, Christen L. Walters Haygood, Chandrika Kurpad, Abhishek Gangrade, Pui-Kai Li, Yonghi Li, Deepak Bhasin, J. Michael Straughn, Donald J. Buchsbaum. STAT3 inhibition by LLL12 in combination with niclosamide and chemotherapy in ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2517. doi:10.1158/1538-7445.AM2014-2517