Vesicular stomatitis virus oncolysis is potentiated by impairing mTORC1-dependent type I IFN production

Abstract

Oncolytic viruses constitute a promising therapy against malignant gliomas (MGs). However, virus-induced type I IFN greatly limits its clinical application. The kinase mammalian target of rapamycin (mTOR) stimulates type I IFN production via phosphorylation of its effector proteins, 4E-BPs and S6Ks. Here we show that mouse embryonic fibroblasts and mice lacking S6K1 and S6K2 are more susceptible to vesicular stomatitis virus (VSV) infection than their WT counterparts as a result of an impaired type I IFN response. We used this knowledge to employ a pharmacoviral approach to treat MGs. The highly specific inhibitor of mTOR rapamycin, in combination with an IFN-sensitive VSV-mutant strain (VSV ΔM51 ), dramatically increased the survival of immunocompetent rats bearing MGs. More importantly, VSV ΔM51 selectively killed tumor, but not normal cells, in MG-bearing rats treated with rapamycin. These results demonstrate that reducing type I IFNs through inhibition of mTORC1 is an effective strategy to augment the therapeutic activity of VSV ΔM51 .innate antiviral immunity | malignant gliomas | mTORC1 | oncolytic viruses M alignant gliomas (MGs) are by far the most frequent, aggressive, and lethal primary brain tumor variants (1, 2). Patients with MGs have a median survival time of approximately 1 y and respond poorly to most available therapeutic modalities (3-5). Thus, more effective treatments are needed.Recent evidence implicates the PI3K/mammalian target of rapamycin (mTOR) signaling pathway as one of the main oncogenic signaling pathways whose deregulation may underlie gliomagenesis (6, 7). mTOR exists in two complexes: mTOR complex 1 (mTORC1), which is sensitive to the drug rapamycin and regulates mRNA translation, and mTORC2, which is rapamycininsensitive and regulates the organization of the actin cytoskeleton (reviewed in refs. 8-10). mTORC1 stimulates type I IFN production via phosphorylation of its target proteins 4E-BPs and S6K1/2 (11). Evidence for the critical role of the mTORC1 signaling pathway in innate immunity emerged from the findings that the mTORC1 inhibitor rapamycin suppresses type I IFN in plasmacytoid dendritic cells (pDCs), which are the major producers of systemic type I IFN (12). In addition, genetic deletion of the mTOR downstream target S6K1/2 leads to impaired type I IFN response (see Results). In contrast, we recently found that the lack of the translational repressors 4E-BP1/2 leads to enhanced type I IFN production (13).Oncogenic transformation is associated with a deficient type I IFN response, which constitutes the first line of defense against virus infection (14,15). Oncolytic viruses are studied as effective anticancer agents because they exploit this selective defect (16)(17)(18)(19). One of the best characterized oncolytic viruses, whose replication is extremely sensitive to the inhibition by IFN, is vesicular stomatitis virus (VSV) (20). However, there are several reasons that limit the use of oncolytic viruses for the treatment of MGs. First, some MGs exhibit a robust type I I...

Enhancing VSV oncolytic activity with an improved cytosine deaminase suicide gene strategy

“…8 Combination strategies using chemotherapeutic compounds and OVs simultaneously are designed to target and increase cancer cell killing, in part, by modulating the antiviral state of the tumor cell or by enhancing the capacity to stimulate apoptosis and/or cell cycle arrest. [9][10][11][12] Histone deacetylase inhibitors or rapamycin have demonstrated enhanced effects on oncolysis, in part, through their capacity to increase OV replication, by dampening the innate antiviral response. 9,11 Increased therapeutic effect has also been achieved under circumstances when viral replication and spreading are not enhanced.…”

“…[9][10][11][12] Histone deacetylase inhibitors or rapamycin have demonstrated enhanced effects on oncolysis, in part, through their capacity to increase OV replication, by dampening the innate antiviral response. 9,11 Increased therapeutic effect has also been achieved under circumstances when viral replication and spreading are not enhanced. 10 Tumor cells encountering 5FU at subtoxic concentrations are altered metabolically by the drug; 34 such cellular changes could potentially affect OV permissiveness.…”

“…VSV has been used in combination with chemotherapeutic agents such as histone deacetylase inhibitors, BCL-2 inhibitors, rapamycin, doxorubicin and other compounds to enhance therapeutic activity. [9][10][11][12] Limitations arising from the use of chemotherapeutic agents include non-selective toxicity in healthy tissues and development of drug resistance. One way to circumvent these restrictions and to further utilize OV combinations is to incorporate a suicide gene strategy that allows specific gene transduction of tumor cells with nonmammalian enzymes that convert innocuous prodrugs into highly toxic chemotherapeutic compounds within the tumor.…”

eIF4E/4E-BP Ratio Predicts the Efficacy of mTOR Targeted Therapies

“…Western blot analysis and cap (m 7 GDP) pull-down assay Cell lysates were prepared, and Western blotting was carried out as described (33). Antibodies against 4E-BP1, 4E-BP2, phospho-4E-BP1 (Thr37/46, Ser65, Thr70), rpS6, phospho-rpS6 (Ser240/244), Akt, phospho-Akt (S473), eIF4G1, and cyclin D3 were from Cell Signaling Technology (Danvers, MA).…”

Suppression of autophagic genes sensitizes CUG2-overexpressing A549 human lung cancer cells to oncolytic vesicular stomatitis virus-induced apoptosis

“…Moreover, one study reported that mTOR signaling stimulates type I IFN production via phosphorylation of its target proteins 4E-BPs and S6 kinase 1/2 (34). MEF cells and mice lacking S6 kinase were more susceptible to VSV infection than their WT counterparts as a result of an impaired type I IFN response (23). On the basis of these results, we speculate that decreased levels of phospho-S6 kinase leads to reduced IFN production, which eventually results in the sensitization to VSV of A549-CUG2 cells treated with Atg5 or Beclin 1 siRNA.…”