Abstract 4193: Lymphotoxin-alpha-armed oncolytic VSV-GP synergizes with SMAC mimetics to induce enhanced tumor cell death and regression

Introduction: Oncolytic viruses (OVs), which selectively replicate in and destroy tumor cells, form a highly promising class of cancer therapeutics with a strong immune stimulatory potential. VSV-GP, a chimeric Vesicular Stomatitis Virus (VSV) pseudotyped with the glycoprotein of the lymphocytic choriomeningitis virus (LCMV) can selectively replicate and express therapeutic cargos in the tumor microenvironment. Lymphotoxin alpha (LTα) - a member of the TNF superfamily - may present as a potent therapeutic cargo based on its immune stimulatory and cell death modulatory characteristics.In this study, we explore the immune promoting and tumor cell death inducing properties of VSV-GP-LTα, a next generation variant with an NF-κB facilitated mode of action. We further investigate clinically relevant combination therapies with “second mitochondria-derived activator of caspases” mimetic compounds (SMCs).

Experimental Procedures: Viral fitness, cargo expression and test substance quality were assessed using growth kinetic, ELISA, RT-qPCR and titration assays. Therapeutic efficacy and safety of VSV-GP-LTα, with or without SMC co-treatment, were assessed in vivo in syngeneic C57BL/6 mice bearing subcutaneous LLC1-IFNAR-/- or B16F10-OVA tumors. To shed further light into the VSV-GP-LTα treatment effects, we applied immunohistochemistry, flow cytometry, multiplex ELISA and Nanostring® assays.

Data Summary: VSV-GP-LTα induced stronger anti-tumor effects and increased overall survival compared to VSV-GP. It was also better tolerated than VSV-GP armed with TNF-α, a therapeutic cargo from the same class. Histological and gene expression analysis confirmed widespread cell killing within the tumor and activation of innate and adaptive immune response markers. However, further characterization of the adaptive immune compartment did not show significant changes induced by the expressed LTα. Building on the observed therapeutic strengths of VSV-GP-LTα, we further explored a treatment combination with SMC. This resulted in a therapeutic synergy with improved treatment-induced tumor cell death, especially in a less permissive tumor setting.

Conclusion: Together, here we show that arming VSV-GP with LTα resulted in a strong inflammation of the tumor microenvironment and enhanced levels of tumor cell death induction. This effect could be further enhanced by the co-treatment with SMC.

Citation Format: Bart Spiesschaert, Philipp Müller, Katharina Angerer, Krishna Das, Tobias Nolden, Carles Urbiola, Judy Ng, Fabian Heinemann, Birgit Stierstorfer, Patrik Erlmann, Guido Wollmann. Lymphotoxin-alpha-armed oncolytic VSV-GP synergizes with SMAC mimetics to induce enhanced tumor cell death and regression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4193.

Chemogenetic ON and OFF switches for RNA virus replication

Therapeutic application of RNA viruses as oncolytic agents or gene vectors requires a tight control of virus activity if toxicity is a concern. Here we present a regulator switch for RNA viruses using a conditional protease approach, in which the function of at least one viral protein essential for transcription and replication is linked to autocatalytical, exogenous human immunodeficiency virus (HIV) protease activity. Virus activity can be en- or disabled by various HIV protease inhibitors. Incorporating the HIV protease dimer in the genome of vesicular stomatitis virus (VSV) into the open reading frame of either the P- or L-protein resulted in an ON switch. Here, virus activity depends on co-application of protease inhibitor in a dose-dependent manner. Conversely, an N-terminal VSV polymerase tag with the HIV protease dimer constitutes an OFF switch, as application of protease inhibitor stops virus activity. This technology may also be applicable to other potentially therapeutic RNA viruses.

The Methyltransferase Region of Vesicular Stomatitis Virus L Polymerase Is a Target Site for Functional Intramolecular Insertion

The L-protein of vesicular stomatitis virus (VSV) is a single-chain multi-domain RNA-dependent RNA polymerase. Previously reported attempts of intramolecular insertions of fluorescent proteins into the L-protein resulted in temperature-sensitive and highly attenuated polymerase activity. Here, we describe a novel insertion site that was selected based on in silico prediction. Of five preselected locations, insertion of the fluorescent protein mCherry in the VSV polymerase between amino acids 1620 and 1621 preserved polymerase function even after extended passaging and showed only mild attenuation compared to wildtype VSV polymerase. High magnification fluorescence imaging revealed a corpuscular cytosolic pattern for the L-protein. To confirm that the insertion site tolerates inclusion of proteins others than mCherry, we cloned mWasabi into the same position in L, generating a VSV-LmWasabi, which was also functional. We also generated a functional dual-color-dual-insertion VSV construct with intramolecularly labeled P and L-proteins. Together, our data present an approach to tag VSV polymerase intramolecularly without perturbing enzymatic activity. This L fusion protein might enable future tracing studies to monitor intracellular location of the VSV transcription and replication machinery in real-time life-imaging studies.

Sprouty2 enhances the tumorigenic potential of glioblastoma cells

Background

Sprouty2 (SPRY2), a feedback regulator of receptor tyrosine kinase (RTK) signaling, has been shown to be associated with drug resistance and cell proliferation in glioblastoma (GBM), but the underlying mechanisms are still poorly defined.

Methods

SPRY2 expression and survival patterns of patients with gliomas were analyzed using publicly available databases. Effects of RNA interference targeting SPRY2 on cellular proliferation in established GBM or patient-derived GBM stemlike cells were examined. Loss- or gain-of-function of SPRY2 to regulate the tumorigenic capacity was assessed in both intracranial and subcutaneous xenografts.

Results

SPRY2 was found to be upregulated in GBM, which correlated with reduced survival in GBM patients. SPRY2 knockdown significantly impaired proliferation of GBM cells but not of normal astrocytes. Silencing of SPRY2 increased epidermal growth factor-induced extracellular signal-regulated kinase (ERK) and Akt activation causing premature onset of DNA replication, increased DNA damage, and impaired proliferation, suggesting that SPRY2 suppresses DNA replication stress. Abrogating SPRY2 function strongly inhibited intracranial tumor growth and led to significantly prolonged survival of U87 xenograft-bearing mice. In contrast, SPRY2 overexpression promoted tumor propagation of low-tumorigenic U251 cells.

Conclusions

The present study highlights an antitumoral effect of SPRY2 inhibition that is based on excessive activation of ERK signaling and DNA damage response, resulting in reduced cell proliferation and increased cytotoxicity, proposing SPRY2 as a promising pharmacological target in GBM patients.

Abstract 2267: Therapeutic synergy of the chimeric, oncolytic virus VSV-GP with immune modulators

Introduction: Oncolytic viruses (OVs), which selectively replicate in and destroy tumor cells, represent a highly promising class of cancer therapeutics. In recent years, the focus in the OV field has significantly shifted from a pure oncolytic mode of action to their strong immune stimulatory potential. Tumor cells lysed by the viruses release pro-inflammatory signals, tumor associated antigens as well as display hallmarks of immunogenic cell death. VSV-GP, a chimeric VSV pseudotyped with the glycoprotein of the lymphocytic choriomeningitis virus (LCMV) is a potent tumor cell-lysing agent and capable of jump-starting α-tumor immunity. The current study explores the immune promoting properties of VSV-GP and investigates clinically relevant combination therapies with checkpoint inhibition (α-PD-1) as well as a “second mitochondria-derived activator of caspases“ mimetic (SMACm).

Experimental Procedures: Immune competent mice bearing established LLC1-IFNARKO, B16-F1-OVA or CT26.CL25-IFNARKO tumors were subject to treatments comprising VSV-GP, α-PD-1, a SMACm or combinations of VSV-GP with either of the latter therapies. α-tumor effects were determined by tumor growth inhibition and/or changes in overall survival. VSV-GP's tumor cell selective replication, resulting in immune activation, was assessed using FFPE based IHC staining for the viral N-protein, PD-L1 and different immune cell subsets as well as the NanoString platform (nCounter Pan Cancer Immune Profiling Panel).

Data Summary: Here we present data on VSV-GP, which displays potent α-tumor efficacy and upon systemic delivery increases the local T-cell infiltration, expression of chemokines, T-cell and myeloid cell specific activation markers as well as expression of immune checkpoints, such as PD-1 and PD-L1 within the tumor microenvironment. Building on the observed therapeutic potential of VSV-GP as monotherapy, its immune promoting properties and the delineated compensatory mechanisms, such as PD-1/-L1 upregulation, we explored therapeutic combinations with a PD-1 blocking antibody, which resulted in a strong improvement of VSV-GP-mediated α-tumor efficacy as well as overall survival. Cured, tumor free animals were protected from tumor rechallange indicating immunological memory formation. We further explored the therapeutic combination of VSV-GP with a SMACm, which also resulted in a strongly improved therapeutic benefit and increased overall survival.

Conclusion: In summary VSV-GP induces a pro-inflammatory microenvironment within infected tumors, increases immune cell infiltration and synergizes with α-PD-1 as well as a SMACm. VSV-GP is a potent OV with a strong α-tumor immunity promoting potential. Preclinical data justify further testing of VSV-GP and the combinations with PD-1 blockade or a SMACm in clinical trials.

Citation Format: Philipp Mueller, Patrik Erlmann, Monika Petersson, Tobias Nolden, Carles Urbiola, Liesa-Marie Schreiber, Bart Spiesschaert, Klaus Erb, Birgit Stierstorfer, Maria Antonietta Impagnatiello, Eric Borges, Knut Elbers, Guido Wollmann, John Park. Therapeutic synergy of the chimeric, oncolytic virus VSV-GP with immune modulators [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2267.

Oncolytic activity of the rhabdovirus VSV-GP against prostate cancer

Oncolytic viruses, including the oncolytic rhabdovirus VSV-GP tested here, selectively infect and kill cancer cells and are a promising new therapeutic modality. Our aim was to study the efficacy of VSV-GP, a vesicular stomatitis virus carrying the glycoprotein of lymphocytic choriomeningitis virus, against prostate cancer, for which current treatment options still fail to cure metastatic disease. VSV-GP was found to infect 6 of 7 prostate cancer cell lines with great efficacy. However, susceptibility was reduced in one cell line with low virus receptor expression and in 3 cell lines after interferon alpha treatment. Four cell lines had developed resistance to interferon type I at different levels of the interferon signaling pathway, resulting in a deficient antiviral response. In prostate cancer mouse models, long-term remission was achieved upon intratumoral and, remarkably, also upon intravenous treatment of subcutaneous tumors and bone metastases. These promising efficacy data demonstrate that treatment of prostate cancer with VSV-GP is feasible and safe in preclinical models and encourage further preclinical and clinical development of VSV-GP for systemic treatment of metastatic prostate cancer.

Abstract B37: VSV-GP: A vaccine vector and oncolytic virus

Oncolytic viruses have recently shown significant clinical benefits in several cancers. Interestingly, in addition to debulking the tumor by direct oncolysis, they were found to act as a cancer vaccine by setting free tumor antigen in the presence of virus-induced danger signals, which have an adjuvant effect. However, as oncolytic viruses induce neutralizing antibodies that inactivate the virus, oncolytic viruses are not delivered efficiently to cancer tissue upon repeated systemic application. Thus, repeated applications of oncolytic viruses have been restricted to intratumoral injections, which clinically has not been convincingly effective in metastatic disease.

We generated the oncolytic virus VSV-GP (Muik et al., Cancer Res, 2014) that is highly potent, lacks toxicity even at high doses (so far tested in mice and rabbits), can be produced at high titers and, above all, does not induce neutralizing antibodies readily. Thus, VSV-GP is unique among the oncolytic viruses in that it can be applied repeatedly without loosing efficacy. VSV-GP is highly effective leading to cure in several cancer mouse models, i.e. malignant glioma, melanoma, prostate cancer and ovarian cancer. In addition to oncolysis, VSV-GP induced a sound anti-tumor immune response and acted synergistically with other cancer immunotherapeutics. Moreover, VSV-GP was shown to be a highly promising vaccine vector and is the only replication competent viral vaccine vector that efficiently boosts the immune response upon repeated application. VSV-GP is thus a highly versatile replication competent viral vector platform for vaccination and cancer therapy.

Citation Format: Alexander Muik, Janine Kimpel, Reinhard Tober, Carles Urbiola, Dorothee von Laer. VSV-GP: A vaccine vector and oncolytic virus. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B37.