Abstract 2275: A novel small molecule, LLL12, inhibits IL-6 induced STAT3 phosphorylation and nuclear translocation

Abstract

Abstract The Signal Transducers and Activators of Transcription (STATs) are a family of cytoplasmic transcription factors, which participate in cellular responses to cytokines and growth factors. STAT3 is found constitutively activated in many types of cancer. Its activation occurs when the Tyrosine residue 705 (Tyr 705) is phosphorylated, monomers form dimmers, and dimmers translocate to the nucleus. Dimerized STAT3 binds to specific DNA response elements and leads to increase the transcription of its downstream genes including angiogenesis, anti-apoptosis, cell cycle progression and proliferation. Therefore, STAT3 is a potential target for cancer therapy. Evidence shows that inhibiting STAT3 using dominant-negative STAT3, antisense oligonucleotides and RNA interference induces tumor cell death. Interleukin 6 (IL-6) is a multifunctional cytokine and its family also comprises cardiotrophine-1 (CT-1), ciliary neurotrophic factor (CNTF), IL-11, leukaemia inhibitory factor (LIF) and oncostatin M (OSM). IL-6 signals through its receptor sIL-6-6R, gp130, Janus kinases (JAKs). A growing numbers of evidence demonstrate that tumorigenesis caused by STAT3 is mediated by IL-6 signals. Therefore, targeting IL-6/STAT3 signaling should be considered for the treatment of patients with higher levels of IL-6/STAT3 signaling. We previously reported that a novel small molecule, LLL12, inhibits STAT3 phosphorylation on Tyr 705 in human cancer cells leading to apoptosis in vitro and suppressed tumor growth in vivo. In this study, we showed that LLL12 also inhibited IL-6 induced STAT3 phosphorylation in human liver and pancreactic cancer cell lines. PANC-1 (pancreatic cancer cell) and Hep3B (liver cancer cell line) were treated with different doses of IL-6 for 30 minutes. Immunofluorecent results showed that IL-6 induced STAT3 phosphorylation on Tyr 705 in these two cancer cell lines. Western blot analysis further indicated that the induction of its phosphorylation was IL-6 dose dependent. To determine whether LLL-12 would inhibit IL-6 induced STAT3 phosphorylation, we pre-treated cells with LLL12 for 2 hours followed by IL-6 treatment for 30 minutes and found that STAT3 phosphorylation was suppressed in cells pre-treated with LLL12. LLL12 pre-treatment also blocked STAT3 translocation to the nucleus. To address whether LLL12 pre-treatment would affect STAT1 phosphorylation, we induced STAT1 with IFN-γ and found that LLL12 did not influence STAT1 phosphorylation. To assess the effects of LLL12 on other factors through IL-6/STAT3 pathway, we analyzed JAKs and observed that IL-6 had no effects on JAK1 phosphorylation, but it induced JAK2 phosphorylation. LLL12 pre-treatment did not suppress JAK2 phosphorylation. In conclusion, structure-based small molecule LLL12 selectively inhibited STAT3 phosphorylation induced by IL-6 and may be a potent agent to target IL-6/STAT3 signaling in cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2275.