STING Restricts oHSV Replication and Spread in Resistant MPNSTs but Is Dispensable for Basal IFN-Stimulated Gene Upregulation

Abstract

Malignant peripheral nerve sheath tumors (MPNSTs) are an aggressive soft-tissue sarcoma amenable only to surgical resection. Oncolytic herpes simplex viruses (oHSVs) are a promising experimental therapy. We previously showed that basal interferon (IFN) and nuclear factor κB (NFκB) signaling upregulate IFN-stimulated gene (ISG) expression and restrict efficient viral infection and cell-to-cell spread in ∼50% of tested MPNSTs. Stimulator of Interferon Genes (STING) integrates DNA sensor activity and mediates downstream IFN signaling in infected cells. We sought to identify STING’s role in oHSV resistance and contribution to basal ISG upregulation in MPNSTs. We show that the level of STING activity in human MPNST cell lines is predictive of oHSV sensitivity and that resistant cell lines have intact mechanisms for detection of cytosolic double-stranded DNA (dsDNA). Furthermore, we show that STING downregulation renders MPNSTs more permissive to oHSV infection and cell-to-cell spread. While next-generation viruses can exploit this loss of STING activity, first-generation viruses remain restricted. Finally, STING is not integral to the previously-observed basal ISG upregulation, indicating that other pathways contribute to basal IFN signaling in resistant MPNSTs. These data broaden our understanding of the intrinsic pathways in MPNSTs and their role in oHSV resistance and offer potential targets to potentiate oncolytic virus activity.

Integrity of the Antiviral STING-mediated DNA Sensing in Tumor Cells Is Required to Sustain the Immunotherapeutic Efficacy of Herpes Simplex Oncolytic Virus

“…Oncolytic virus spread, assessed by viral-encoded eGFP expression, evidenced the formation of large lysis plaques in Sting knockout cells, compared to the viral restraint observed in the Sting wild-type statuses of both parental cell lines ( Figure 2 A,B). Interestingly, as reported in the independent scientific literature [ 24 , 25 , 26 , 27 ], we confirmed that the efficiency of viral replication is actually related to Sting expression, since Sting knock down cells show an intermediate level of viral replication, compared to Sting wild-type and knockout cells ( Figure S4 ).…”

“…These data demonstrate that Sting pathway efficiently counteracts the infection of HSV-1, even in the presence of functional viral anti- Sting genes (e.g., γ34.5) held by the non-attenuated R-LM113 and R-LM55 viruses [ 16 , 27 ]. Altogether, these data suggest that tumor cells with impaired DNA-sensing Sting pathway could potentially represent an improved target for oncolytic virotherapy.…”

“…Considering the aforementioned evidence, the loss-of-function in STING -mediated DNA sensing that occurs in tumor cells to escape immune surveillance is thought to represent the Achilles’ heel that makes cancer an exquisite target of oncolytic viruses [ 24 , 25 , 26 , 27 , 48 ]. These speculations have been addressed in xenografts in nude mice which, however, do not keep under consideration the tumor-resident function of STING in inducing an antitumor immune response that is still a limitedly explored topic [ 25 , 26 ].…”

“…Finally, based on the STING-dependent susceptibility of mammalian cells to HSV-1 and additional viruses, it can be predicted that genetic variants of STING could contribute to human susceptibility to viral infections by both DNA and RNA viruses [ 13 , 25 , 26 , 27 ]. In particular, future efforts could reveal the susceptibility of human cells carrying STING variants to the coronavirus SARS-CoV-2 (formerly 2019-nCoV) which is currently responsible for the COVID-19 pandemic.…”

“…Despite this evidence supporting the application of oncovirotherapy to a wider spectrum of cancer indications, the role of innate antiviral response in establishing adaptive antitumor immunity needs to be evaluated in immunocompetent models. In this field, recent evidence demonstrates that STING low (knock down) compared to STING high cancer cells are slightly more susceptible to lysis and still succumb in an immunogenic way following treatment with T-VEC [ 27 , 28 ], but the complete loss of STING that often occurs in cancer cells needs to be assessed.…”