STAT1 and NF-κB Inhibitors Diminish Basal Interferon-Stimulated Gene Expression and Improve the Productive Infection of Oncolytic HSV in MPNST Cells

Abstract

Interferon stimulated genes (ISGs) encode diverse proteins that mediate intrinsic antiviral resistance in infected cells. Here it was hypothesized that malignant peripheral nerve sheath tumor (MPNST) cells resist the productive infection of oncolytic herpes simplex virus (oHSV) through activation of the JAK/STAT1 pathway and resultant upregulation of ISGs. Multiple human and mouse MPNST cells were used to explore the relationship between STAT1 activation and the productive infection of Δγ-134.5 oHSVs. STAT1 activation in response to oHSV infection was found to associate with diminished Δγ-134.5 oHSVs replication and spread. Multi-day pre-treatment, but not co-treatment, with a JAK inhibitor significantly improved viral titer and spread. ISG expression was found to be elevated prior to infection and downregulated when treated with the inhibitor, suggesting that the JAK/STAT1 pathway is active prior to infection. Conversely, upregulation of ISG expression in normally permissive cells significantly decreased oHSV productivity. Finally, a possible link between NFκB pathway activation and ISG expression was established through the expression of inhibitor of kB (IκB) which decreased basal STAT1 transcription and ISG expression. These results demonstrate that basal ISG expression prior to infection contributes to the resistance of Δγ-134.5 oHSVs in MPNST cells. Implications While cancer-associated ISG expression has been previously reported to impart resistance to chemotherapy and radiotherapy, these data show that basal ISG expression also contributes to oncolytic HSV resistance.

Pre-clinical Assessment of C134, a Chimeric Oncolytic Herpes Simplex Virus, in Mice and Non-human Primates

“…IRF3 and HSV antigen were less prominent in the parenchyma of Δγ 1 34.5-treated mice. This is consistent with our previous findings showing that C134, like its parent Δγ 1 34.5 virus, induces early IRF3 and interferon (IFN) signaling and supports our hypothesis that this enhanced IFN response is linked to C134 aneurovirulence 17, 18…”

“…Next, to identify whether a C134 and WT-HSV recombination event could produce a more virulent virus, we created a WT HSV encoding HCMV IRS1 and tested it in murine neurotoxicity studies. The results show that IRS1 expression does not increase WT HSV-1 virulence and suggest that the resulting IFN response limits C134 replication spread, consistent with our past studies 17, 18. Together, these data support advancing C134 for production of a clinical-grade product for phase I clinical trials.…”

“…We previously demonstrated that the C134 virus induces an IRF3-mediated anti-viral response and that type I IFN limits C134 replication and cell-to-cell spread 17, 18. We hypothesized that this IFN response limited C134 replication and spread in the CNS 17, 18.…”

“…We hypothesized that this IFN response limited C134 replication and spread in the CNS 17, 18. To examine the kinetics of the IFN-mediated anti-viral activity elicited by C134 replication and spread in the CNS, we performed two studies.…”

Oncolytic herpes simplex virus interactions with the host immune system

“…The type I IFN (IFN-α/β) signaling pathway is critical in suppressing HSV replication and pathogenicity [25**], and orchestrating innate immune responses [15]. STAT1 activation in infected malignant peripheral nerve sheath tumor (MPNST) cells, with induction of IFN-stimulated genes (ISGs), was associated with reduced oHSV R3616 (γ34.5Δ) replication, while JAK inhibitor ruxolitinib increased virus yield [26]. STAT3, as opposed to STAT1 and STAT2, is an important negative regulator of type I IFN signaling and is activated in many tumors [27].…”