Clonal variation in interferon response determines the outcome of oncolytic virotherapy in mouse CT26 colon carcinoma model

Abstract

In our earlier studies, Semliki Forest virus vector VA7 completely eliminated type I interferon (IFN-I)-unresponsive human U87-luc glioma xenografts, whereas interferon-responsive mouse gliomas proved refractory. Here, we describe in two clones of CT26 murine colon carcinoma, opposed patterns of IFN-I responsiveness and sensitivity to VA7. Both CT26WT and CT26LacZ clones secreted biologically active interferon in vitro upon virus infection but only CT26WT cells were protected. Focal infection of CT26WT cultures was self-limiting but could be rescued using IFN-I pathway inhibitor Ruxolitinib or antibody against IFNβ. Whole transcriptome sequencing (RNA-Seq) and protein expression analysis revealed that CT26WT cells constitutively expressed 56 different genes associated with pattern recognition and IFN-I signaling pathways, spanning two reported anti-RNA virus gene signatures and 22 genes with reported anti-alphaviral activity. Whereas CT26WT tumors were strictly virus-resistant in vivo, infection of CT26LacZ tumors resulted in complete tumor eradication in both immunocompetent and severe combined immune deficient mice. In double-flank transplantation experiments, CT26WT tumors grew despite successful eradication of CT26LacZ tumors from the contralateral flank. Tumor growth progressed uninhibited also when CT26LacZ inoculums contained only a small fraction of CT26WT cells, demonstrating dominance of IFN responsiveness when heterogeneous tumors are targeted with interferon-sensitive oncolytic viruses.

MicroRNA-Attenuated Clone of Virulent Semliki Forest Virus Overcomes Antiviral Type I Interferon in Resistant Mouse CT-2A Glioma

“…8) and others (13) show functional IFN-I signaling. Of note, even a small fraction of cells in the heterogeneous tumor tissue capable of IFN-I signaling can promote resistance to virotherapy (8).…”

“…L10 virus was propagated from original infectious stock (kindly provided by John Fazakerley). Virus titration was done by plaque assay in Vero(B) cells as described elsewhere (8). CT-2A-Fluc plaque assay.…”

“…In addition, GBM cells, GBM stem cell-like cells, and infiltrating leukocytes may mount a strong innate response against the virus. In particular, viruses whose selectiveness for cancer tissue relies on defective type I interferon (IFN-I) signaling in tumor cells may completely lose efficacy (8).…”

Safe and Effective Treatment of Experimental Neuroblastoma and Glioblastoma Using Systemically Delivered Triple MicroRNA-Detargeted Oncolytic Semliki Forest Virus

“…6C). As previously observed, in clones of mouse colon carcinoma, CT26WT and CT26LacZ differential expression of ISGs can contribute to dramatic difference in the efficacy of SFV therapy (40). ISG expression in CT-2A and GL261 is unknown, which may be a reason for the observed difference in oncolytic response.…”

Oncolytic Alphaviruses in Cancer Immunotherapy

“…Unexpectedly, both SFV and VV were unable to infect parenchymal brain tumors in mice. These findings triggered the investigation on clonal variation on interferon responses [79]. Two SFV VA7-sensitive clones of CT26 mouse colon carcinoma were evaluated for tumor regression.…”