Z Gastroenterol 2014; 52 - G1
DOI: 10.1055/s-0034-1386661

Targeting RIG-I with 5'ppp-modified RNA for immunotherapy of hepatocellular carcinoma (HCC)

L Posselt 1, I Lazic 1, A Funk 1, S Kirchleitner 1, S Schievenbusch 1, T Adunka 1, S Endres 1, P Düwell 1, S Rothenfusser 1, M Schnurr 1
  • 1Klinische Pharmakologie, Medizinische Klinik und Poliklinik IV, Campus Innenstadt, München

Background: HCC is the most common primary malignant type of liver cancer. Median survival for patients with advanced tumors is less than one year. Novel treatment options are urgently needed. The cytosolic helicase retinoic acid-inducible gene I (RIG-I) is an immune receptor for viral 5'-triphosphat-RNA (ppp-RNA) and its activation leads to innate and adaptive immunity via type I IFN and proinflammatory cytokines. In addition, it promotes the intrinsic pathway of apoptosis in tumor cells. This project focuses on the development of 5'ppp-RNAs targeting RIG-I for HCC therapy.

Methods: A synthetic 5'ppp-RNA was generated via in vitro transcription and used to analyze functional RIG-I expression in human (Hep3B) and murine (Hepa1 – 6) HCC cells. Therapeutic efficacy was evaluated in vivo in the orthotopic Hepa1 – 6 mouse model of HCC. Seven days after tumor induction mice were treated intravenously with 5'ppp-RNA complexed to polyethylenimine. 24h later mice were sacrificed, tumors removed and size measured. Tumor cell death was assessed by TUNNEL staining and cytokine expression by qRT-PCR. In another experiment survival of RNA-treated mice was monitored.

Results: Treatment of human and murine HCC cells with ppp-RNA induced phosphorylation of IRF3, production of IFN-β and IFN-induced genes, such as CXCL10, indicative of intact RIG-I signaling. In addition, RIG-I activation led to profound tumor cell death. A single treatment of mice with orthotopic HCC with ppp-RNA significantly reduced tumor size in comparison to control RNA, induced type I IFN production in the tumor tissue and led to massive tumor cell death. Treatment of mice with repeated ppp-RNA injections significantly prolonged survival.

Conclusion: We could demonstrate that the RIG-I pathway is functional in HCC cells. RIG-I activation leads to type I IFN production and massive tumor cell death both in vitro and in vivo. RIG-I-based immunotherapy holds promise for HCC therapy deserving further evaluation.