Therapeutic Efficacy of Bifunctional siRNA Combining TGF-β1 Silencing with RIG-I Activation in Pancreatic Cancer

• Published in: Cancer research (Chicago, Ill.) Ill.), 2013-03, Vol.73 (6), p.1709-1720
• Main Authors: ELLERMEIER, Jonathan, JIWU WEI, HARTMANN, Gunther, ENDRES, Stefan, SCHNURR, Max, DUEWELL, Peter, HOVES, Sabine, STIEG, Mareike R, ADUNKA, Tina, NOERENBERG, Daniel, ANDERS, Hans-Joachim, MAYR, Doris, POECK, Hendrik
• Format: Article
• Language: English
• Subjects: Animals; Antineoplastic agents; Apoptosis; Biological and medical sciences; CD8-Positive T-Lymphocytes - immunology; Chemokine CXCL10 - blood; DEAD Box Protein 58; DEAD-box RNA Helicases - metabolism; Enzyme-Linked Immunosorbent Assay; Female; Flow Cytometry; Gastroenterology. Liver. Pancreas. Abdomen; Gene Silencing; Interferon Type I - blood; Liver. Biliary tract. Portal circulation. Exocrine pancreas; Medical sciences; Mice; Mice, Inbred C57BL; Multiple tumors. Solid tumors. Tumors in childhood (general aspects); Pancreatic Neoplasms - genetics; Pancreatic Neoplasms - immunology; Pancreatic Neoplasms - metabolism; Pancreatic Neoplasms - pathology; Pharmacology. Drug treatments; Real-Time Polymerase Chain Reaction; RNA, Small Interfering - genetics; RNA, Small Interfering - therapeutic use; Signal Transduction; Transforming Growth Factor beta1 - genetics; Tumors
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.CAN-11-3850

Deregulated TGF-β signaling in pancreatic cancer promotes tumor growth, invasion, metastasis, and a potent immunosuppressive network. A strategy for disrupting this tumor-promoting pathway is silencing TGF-β by siRNA. By introducing a triphosphate group at the 5' end of siRNA (ppp-siRNA), gene silencing can be combined with immune activation via the cytosolic helicase retinoic acid-inducible gene I (RIG-I), a ubiquitously expressed receptor recognizing viral RNA. We validated RIG-I as a therapeutic target by showing that activation of RIG-I in pancreatic carcinoma cells induced IRF-3 phosphorylation, production of type I IFN, the chemokine CXCL10, as well as caspase-9-mediated tumor cell apoptosis. Next, we generated a bifunctional ppp-siRNA that combines RIG-I activation with gene silencing of TGF-β1 (ppp-TGF-β) and studied its therapeutic efficacy in the orthotopic Panc02 mouse model of pancreatic cancer. Intravenous injection of ppp-TGF-β reduced systemic and tumor-associated TGF-β levels. In addition, it induced high levels of type I IFN and CXCL10 in serum and tumor tissue, systemic immune cell activation, and profound tumor cell apoptosis in vivo. Treatment of mice with established tumors with ppp-TGF-β significantly prolonged survival as compared with ppp-RNA or TGF-β siRNA alone. Furthermore, we observed the recruitment of activated CD8(+) T cells to the tumor and a reduced frequency of CD11b(+) Gr-1(+) myeloid cells. Therapeutic efficacy was dependent on CD8(+) T cells, whereas natural killer cells were dispensable. In conclusion, combing TGF-β gene silencing with RIG-I signaling confers potent antitumor efficacy against pancreatic cancer by breaking tumor-induced CD8(+) T cell suppression.