Therapeutic efficacy of bifunctional siRNA combining TGF-β1 silencing with RIG-I activation in pancreatic cancer
Menée in vitro et in vivo, cette étude évalue l'activité antitumorale d'un petit ARN-interférent, qui réduit au silence le gène TGF-β1 tout en activant la signalisation RIG-I, pour le traitement d'un cancer du pancréas
Deregulated transforming growth factor-β (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 small interfering RNA (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 interferon (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 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 to 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 NK cells were dispensable. In conclusion, combing TGF-β gene silencing with RIG-I signaling confers potent anti-tumor efficacy against pancreatic cancer by braking tumor-induced CD8+ T cell suppression.