EGCG Enhances the Therapeutic Potential of Gemcitabine and CP690550 by Inhibiting STAT3 Signaling Pathway in Human Pancreatic Cancer Su-Ni Tang1, Junsheng Fu2, Sharmila Shankar2, Rakesh K. Srivastava1* 1 Department of Pharmacology, Toxicology and Therapeutics, and Medicine, The University of Kansas Cancer Center, The University of Kansas Medical Center, Kansas City, Kansas, United States of America, 2 Department of Pathology and Laboratory Medicine, The University of Kansas Cancer Center, The University of Kansas Medical Center, Kansas City, Kansas, United States of America Abstract Background: Signal Transducer and Activator of Transcription 3 (STAT3) is an oncogene, which promotes cell survival, proliferation, motility and progression in cancer cells. Targeting STAT3 signaling may lead to the development of novel therapeutic approaches for human cancers. Here, we examined the effects of epigallocathechin gallate (EGCG) on STAT3 signaling in pancreatic cancer cells, and assessed the therapeutic potential of EGCG with gemcitabine or JAK3 inhibitor CP690550 (Tasocitinib) for the treatment and/or prevention of pancreatic cancer. Methodology/Principal Findings: Cell viability and apoptosis were measured by XTT assay and TUNEL staining, respectively. Gene and protein expressions were measured by qRT-PCR and Western blot analysis, respectively. The results revealed that EGCG inhibited the expression of phospho and total JAK3 and STAT3, STAT3 transcription and activation, and the expression of STAT3-regulated genes, resulting in the inhibition of cell motility, migration and invasion, and the induction of caspase-3 and PARP cleavage. The inhibition of STAT3 enhanced the inhibitory effects of EGCG on cell motility and viability. Additionally, gemcitabine and CP690550 alone inhibited STAT3 target genes and synergized with EGCG to inhibit cell viability and induce apoptosis in pancreatic cancer cells. Conclusions/Significance: Overall, these results suggest that EGCG suppresses the growth, invasion and migration of pancreatic cancer cells, and induces apoptosis by interfering with the STAT3 signaling pathway. Moreover, EGCG further enhanced the therapeutic potential of gemcitabine and CP690550 against pancreatic cancer. Citation: Tang S-N, Fu J, Shankar S, Srivastava RK (2012) EGCG Enhances the Therapeutic Potential of Gemcitabine and CP690550 by Inhibiting STAT3 Signaling Pathway in Human Pancreatic Cancer. PLoS ONE 7(2): e31067. doi:10.1371/journal.pone.0031067 Editor: Hana Algu¨ l, Technische Universita¨t M u¨nchen, Germany Received May 11, 2011; Accepted January 1, 2012; Published February 13, 2012 Copyright: 2012 Tang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported in part by the grants from the National Institutes of Health (R01CA125262,RO1CA114469 and RO1CA125262-02S1) and the Kansas Bioscience Authority. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: rsrivastava@kumc.edu Introduction Signal transduction and activators of transcription (STAT) proteins is a family of cytoplasmic transcription factors which are initially present in inactive forms [1,2]. They are stimulated by the binding of signaling peptides, such as cytokine, growth factors, and hormone, which results in dimerization of their cognate receptors and activation of tyrosine kinases such as Janus kinase (JAK). The activated tyrosine kinases could subsequently phosphorylate the cytoplasmic domains of receptors to provide recognition sites for non-phosphorylated STATs monomers. Once STATs are phos- phorylated by activated tyrosine kinases after binding, they form homo or hetero-dimers via their Src-homology 2 (SH2) domain and rapidly migrate into the nucleus, where the dimers bind to DNA sequences to active specific gene transcription [1,2]. Numerous experiments have demonstrated that normal physical functions of STATs are critical in regulating many aspects of cellular proliferation, differentiation, migration, and survival. Among all the STAT family members, STAT3 is the most intimately linked to cell survival and proliferation and tumorigen- esis [3,4]. It is widely expressed in most tissues and is considered as a potential oncogene. STAT3 is often constitutively active in many human cancer cells, including multiple myeloma, glioblastoma, leukemia, lymphoma, breast cancer, prostate cancer, lung cancer, and neck cancer [5,6,7]. STAT3 can be activated by multiple cytokines, including IL-6, IL-11, ciliary neurotrophic factor, and leukemia inhibitory factor, which all use gp130-type receptors. Interestingly, STAT3 can contribute to either apoptosis or survival in different organs and cell types. It can promote the proliferation in hepatocytes [8], neuron cells [9], and T cells [10], but is indispensable for the apoptosis in mammary [11] and myeloid cells [12]. STAT3 is a latent transcription factor that resides in the cytoplasm. Upon activation by tyrosine phosphorylation, STAT3 dimerizes, translocates to the nucleus and binds to nuclear DNA to modulate transcription of target genes. STAT3 phosphorylation is principally mediated through the activation of non-receptor protein tyrosine kinase family of JAKs, which include many PLoS ONE | www.plosone.org 1 February 2012 | Volume 7 | Issue 2 | e31067