Abstract 4073: STAT3 inhibitors elicit direct anti-tumor effects against human biliary caner cell lines and limit release of immune suppressive cytokines in vitro

Abstract

Abstract Biliary cancer (BC), or cholangiocarcinoma originates from the malignant transformation of epithelial cells in the bile ducts. This deadly cancer is typically refractory to standard therapies and has a 3 year survival rate of only 10%. Therefore, novel treatment strategies are desparately needed against this malignancy. One important feature of BC cells is their ability to secrete interleukin-6 (IL-6) in an autocrine manner. This characteristic affords them an opportunity to activate numerous pro-oncogenic signaling pathways including MAPK, and STAT3 within the tumor cell, while simultaneously promoting immunologic changes in patients with advanced disease. We hypothesized that inhibitors of Signal-Transducer and Activator of Transcription-3 (STAT3) pathway may elicit a dual effect by promoting apoptosis of human BC cell lines, and limiting the secretion of immunosuppressive cytokines from these cells. A panel of human BC cell lines with various genotypic profiles was utilized, and all demonstrated secretion of IL-6 (range 5149-68pg/mL) and had constitutively phosphorylated STAT3 as determined by western blot. Similar to positive control conditions with IL-6 + GM-CSF (10 ng/mL each), exposure of human peripheral blood mononuclear cells to 5% or 10% BC culture supernatants induced in vitro differentiation into myeloid derived suppressor cells (MDSC). These data indicate that BC cells have robust activation of the IL-6/STAT3 signaling axis, and that culture supernatants contain factors capable of promoting expansion of immune suppressive cell subsets. A novel small molecule inhibitor FLLL100, could directly inhibit Tyr705 phosphorylation within the SH2 domain of STAT3, and induce apoptosis in the BC cell lines regardless of genotypic profile. Both growth inhibitory (by MTT assay) and pro-apoptotic effects (by Annexin V/PI staining) were observed within 24-48 hours of drug exposure at micromolar concentrations. Apoptosis was confirmed after drug exposure by assessment of PARP cleavage by immunoblot. Exposure of BC cell lines to FLLL100 resulted in significantly reduced secretion of immunomodulatory cytokines including IL-6 (p<0.05) and GM-CSF (p<0.05) in culture supernatants. Together, these data indicate that the IL-6/STAT3 signaling axis plays a role in human BC survival and that targeting this pathway can limit immune suppressive factors derived from BC cell lines. Citation Format: Jennifer Yang, Kaitlin Keenan, Thomas Mace, Tanios Bekaii-Saab, James Fuchs, Eric Schwartz, Chenglong Li, Jiayuh Lin, Pui-Kai Li, Gregory Lesinski. STAT3 inhibitors elicit direct anti-tumor effects against human biliary caner cell lines and limit release of immune suppressive cytokines in vitro. [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 4073. doi:10.1158/1538-7445.AM2014-4073