Oncolytic Newcastle Disease Virus Expressing a Checkpoint-Inhibiting Antibody As a Radiosensitizing Immunotherapy in a Murine Melanoma Model

Abstract

Monoclonal antibodies targeting negative regulators, or checkpoint molecules (e.g. PD1 or CTLA4), of antitumor T cells have clinical efficacy in treating malignant disease. Many patients enjoy remarkable responses to the combination of radiotherapy with checkpoint inhibitors; however, the majority of patients treated derives little long-term clinical benefit. Multimodal therapies with synergistic mechanisms of action may be needed to enhance tumor immunogenicity. Both Newcastle disease virus & radiotherapy induce antitumor immunity in combination with checkpoint blockade in murine melanoma models. The efficacy of combining an oncolytic virus & radiotherapy with checkpoint blockade has not been evaluated in animal models to our knowledge. In vitro, B16-F10 cells were infected with Newcastle disease virus, irradiated (0, 2, 4, 8, 16 or 32 Gy), and assayed for cell survival. In vivo, B16-F10 melanoma flank tumors were implanted in C57BL/6 or athymic mice. Newcastle disease virus & radiotherapy were evaluated individually and in combination for their ability to control advanced tumors in mice receiving systemic checkpoint inhibitors (anti-PD1 or anti-CTLA4 monoclonal antibodies). Mice received a single fraction of radiation (0, 5, 10 or 20 Gray) on treatment day 0, and Newcastle disease virus was administered via intratumoral injection (days 0, 2, 4, 8 & 10). Recombinant Newcastle disease virus expressing an anti-CTLA4 antibody was used to assess the efficacy of local checkpoint blockade compared to systemic administration. Tumor volumes and survival were assayed. Newcastle disease virus & radiotherapy work in combination to enhance tumor clearance and survival in a murine melanoma model. The combination is superior to either radiotherapy or Newcastle disease virus alone and is most effective in immunocompetent animals with the addition of a checkpoint inhibitor. Recombinant Newcastle disease virus expressing an anti-CTLA4 mAb has comparable efficacy to systemically delivered anti-CTLA4 plus wild-type Newcastle disease virus. Both in vitro or in athymic mice, NDV infected B16-F10 cells were more sensitive to radiation than uninfected cells or tumors, respectively. Recombinant Newcastle disease virus enhances tumor immunogenicity while serving as a radiosensitizing agent. This combination has the potential to enhance tumor immunogenicity while deescalating systemic immunotherapy or radiation dose to improve toxicity. Experiments in vitro and in athymic mice demonstrate potential for NDV as a radiosensitizer in immunodeficient cohorts.