Spector, I., Institute of Animal Sciences, The Volcani Center, Bet Dagan, Israel, Department of Animal Sciences, Hebrew University of Jerusalem, Rehovot, Israel
Zilberstein, Y., The Sackler Cellular and Molecular Imaging Center (SCMIC), Tel Aviv University, Tel Aviv, Israel
Lavy, A., Institute of Animal Sciences, The Volcani Center, Bet Dagan, Israel, Department of Animal Sciences, Hebrew University of Jerusalem, Rehovot, Israel
Nagler, A., Department of Hematology and Bone Marrow Transplantation, Chaim Sheba Medical Center, Tel Hashomer, Israel
Genin, O., Institute of Animal Sciences, The Volcani Center, Bet Dagan, Israel
Pines, M., Institute of Animal Sciences, The Volcani Center, Bet Dagan, Israel

Introduction: Stroma cells and extracellular matrix (ECM) components provide the pivotal microenvironment for tumor development. The study aimed to evaluate the importance of the pancreatic stroma for tumor development. Methods: Pancreatic tumor cells were implanted subcutaneously into green fluorescent protein transgenic mice, and stroma cells invading the tumors were identified through immunohistochemistry. Inhibition of tumor invasion by stroma cells was achieved with halofuginone, an inhibitor of TGFβ/Smad3 signaling, alone or in combination with chemotherapy. The origin of tumor ECM was evaluated with species-specific collagen I antibodies and in situ hybridization of collagen α1(I) gene. Pancreatic fibrosis was induced by cerulean injection and tumors by spleen injection of pancreatic tumor cells. Results: Inhibition of stroma cell infiltration and reduction of tumor ECM levels by halofuginone inhibited development of tumors derived from mouse and human pancreatic cancer cells. Halofuginone reduced the number only of stroma myofibroblasts expressing both contractile and collagen biosynthesis markers. Both stroma myofibroblasts and tumor cells generated ECM that contributes to tumor growth. Combination of treatments that inhibit stroma cell infiltration, cause apoptosis of myofibroblasts and inhibit Smad3 phosphorylation, with chemotherapy that increases tumor-cell apoptosis without affecting Smad3 phosphorylation was more efficacious than either treatment alone. More tumors developed in fibrotic than in normal pancreas, and prevention of tissue fibrosis greatly reduced tumor development. Conclusions: The utmost importance of tissue fibrosis and of stroma cells for tumor development presents potential new therapy targets, suggesting combination therapy against stroma and neoplastic cells as a treatment of choice. © 2012 Spector et al.