Abstract 4358: The immunomodulatory anticancer agent RRx-001 induces a vaccine-like interferon response through epigenetic induction of viral mimicry

Abstract

Abstract RRx-001, sourced from the aerospace industry and currently in phase II clinical trials, is a novel anti-cancer agent that mediates immunomodulatory effects, either directly through polarization of tumor associated macrophages or indirectly through vascular normalization and increased T-lymphocyte infiltration. With multiple additional mechanisms of action including upregulation of oxidative stress, depletion of GSH and NADPH, anti-angiogenesis and epigenetic modulation, RRx-001 is being studied as a single chemotherapeutic agent to resensitize tumors to prior therapy and to prime tumors to respond to radiation, chemotherapy and immunotherapy in combination therapy studies. In this study, we identified another mechanism, viral mimicry, which refers to the ‘unsilencing’ of epigenetically repressed viral genes present in the tumor that provokes an immune response and may contribute to the anti-cancer activity of RRx-001. Specifically, RRx-001 inhibited the growth of human colon cancer cells (HCT 116) and decreased levels of the DNA methyltransferases Dnmt1 and Dnmt3a in a time and dose-dependent manner. Treatment of HCT 116 cells with 0.5 μM RRx-001 for 24 hours significantly increased transcripts of interferon (IFN)-responsive genes and this induction was sustained for up to 4 weeks after transient exposure to RRx-001. ELISA assays showed that RRx-001 increased secretion of type I and III IFNs by HCT 116 cells, and these IFNs were confirmed to be bioactive. Transcription of endogenous retroviruses was induced by RRx-001 through demethylation of the promoter of endogenous retrovirus genes as determined by methylation-specific polymerase chain reaction and combined bisulfite restriction analysis. Immunofluorescence staining with J2 antibody confirmed induction of double-stranded RNA. In conclusion, transient exposure of HCT 116 cells to low-dose RRx-001 induced transcription of silenced retroviral genes present in the cancer cell DNA with subsequent synthesis of IFN in response to this “pseudo-pathogenic” stimulus, mimicking an antiviral defense. RRx-001-mediated IFN induction may have the potential to improve the efficacy of immunotherapies as well as radiotherapy, standard chemotherapies and molecularly targeted agents when used in combination. Citation Format: Hongjuan Zhao, Shoucheng Ning, Rosalie Nolley, Jan Scicinski, Bryan Oronsky, Susan J. Knox, Donna M. Peehl. The immunomodulatory anticancer agent RRx-001 induces a vaccine-like interferon response through epigenetic induction of viral mimicry [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4358. doi:10.1158/1538-7445.AM2017-4358