Microenvironment and Immunology Neutralizing Murine TGFbR2 Promotes a Differentiated Tumor Cell Phenotype and Inhibits Pancreatic Cancer Metastasis

Elevated levels of TGFb are a negative prognostic indicator for patients diagnosed with pancreatic cancer; as a result, the TGFb pathway is an attractive target for therapy. However, clinical application of pharmacologic inhibition of TGFb remains challenging because TGFb has tumor suppressor functions in many epithelial malignancies, including pancreatic cancer. In fact, direct neutralization of TGFb promotes tumor progression of genetic murine models of pancreatic cancer. Here, we report that neutralizing the activity of murine TGFb receptor 2 using a monoclonal antibody (2G8) has potent antimetastatic activity in orthotopic human tumor xenografts, syngeneic tumors, and a genetic model of pancreatic cancer. 2G8 reduced activated fibroblasts, collagen deposition,microvessel density, and vascular function. These stromal-specific changes resulted in tumor cell epithelial differentiation and a potent reduction in metastases. We conclude that TGFb signaling within stromal cells participates directly in tumor cell phenotype and pancreatic cancer progression. Thus, strategies that inhibit TGFb-dependent effector functions of stromal cells could be efficacious for the therapy of pancreatic tumors. Cancer Res; 74(18); 4996–5007. 2014 AACR. Introduction Pancreatic cancer, the fourth leading cause of cancer-related mortality, presents a formidable challenge for treatment (1). Early metastasis, aggressive tumor biology, and a stromal rich microenvironment provide potentialmechanisms for the resistance of pancreatic cancer to conventional chemotherapy. Recent work suggests that stromal cells within the tumor microenvironment are critical determinants of tumor development, progression, and metastasis (2, 3). Therefore, there is heightened interest in strategies that target stromal cells, including cancer-associated fibroblasts, immune cells, and vascular cells. Numerous cytokines participate in the progression of pancreatic malignancies. In particular, TGFb has a complex function in pancreatic ductal adenocarcinoma (PDA). TGFb is known to inhibit tumor progression in early stages of PDA development yet, at later stages, TGFb functions as a tumor promoter (4). The features that underlie the switch of TGFb from a tumor suppressor to a tumor promoter in PDA are unclear. Mutations in the TGFb signaling pathway occur in a large percentage (>50%) of human PDA (5) and likely contribute to the TGFb functional switch. This has been modeled in mice where alterations of the TGFb pathway (e.g., deletion of Smad4 or Tgfbr2) cooperated with activated Kras to promote disease progression (6–8). Furthermore, elevated expression of TGFb, which is frequent in PDA can promote tumor development, tumor cell epithelial-to-mesenchymal transition (EMT), and tumor cell survival and motility (9–12). TGFb also induces immunosuppression, activation of fibroblasts, angiogenesis, and collagen deposition (13, 14). Therefore, specifically targeting the protumoral aspects of TGFbmight provide therapeutic efficacy. Pharmacologic strategies that block TGFb activity have been explored in preclinical models of pancreatic cancer (reviewed in ref. 15). As discussed by Achyut and Yang (15), targeting the TGFb pathway alters the tumor microenvironment and the outcome of therapy might be more dependent upon microenvironmental actions than on direct tumor cell effects. Previously, 2G8 (aka MT1), a monoclonal antibody against mouse TGFb receptor 2 (Tgfbr2), reduced primary tumor growth and metastasis in several syngenic models of breast cancer, primarily through its effects on tumor cells and tumorassociated immune cells (16). Given the clinical importance of TGFb dysregulation in PDA (15), we hypothesized that stromal Tgfbr2 inhibition could be effective in mouse models of PDA. Given that 2G8 is mouse-specific, we implemented this antibody in human xenograft models of PDA to specifically target stromal Tgfbr2 without interrupting TGFb signaling in the Division of Surgical Oncology, Department of Surgery, University of Texas Southwestern Medical Center, Dallas, Texas. Hamon Center for Therapeutic Oncology Research, University of Texas Southwestern Medical Center, Dallas, Texas. Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas. Imclone Systems (a wholly owned subsidiary of Eli Lilly and Company), New York, New York. Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas. Corresponding Author: Rolf A. Brekken, Hamon Center for Therapeutic Oncology Research, University of Texas Southwestern Medical Center, 6000Harry Hines Blvd, Dallas, TX 75390-8593. Phone: 214-648-5151; Fax: 214-648-4940; E-mail: [email protected] doi: 10.1158/0008-5472.CAN-13-1807 2014 American Association for Cancer Research. Cancer Research Cancer Res; 74(18) September 15, 2014 4996 on July 22, 2017. © 2014 American Association for Cancer Research. cancerres.aacrjournals.org Downloaded from Published OnlineFirst July 24, 2014; DOI: 10.1158/0008-5472.CAN-13-1807