Oncolytic adenoviral therapy demonstrates efficacy in murine models of melanoma brain metastases
Introduction
Amongst all solid cancers, melanoma brain metastases (MBM) have the highest likelihood of metastasizing to the brain. The emergence of immune checkpoint inhibitors (ICI) for metastatic melanoma have demonstrated increasingly promising results, particularly for extracranial disease, through reversal of immune cell exhaustion and T cell mediated tumor killing. However, intracranial progression remains a challenging obstacle and is a frequent cause of tumor-related death. Thus, there is a critical need to develop novel treatment strategies for these brain metastasis patients. Oncolytic viral (OV) therapy leverages tumor cell replication machinery to selectively replicate and kill tumor cells, modulate immune cell composition in the tumor microenvironment (TME), and promote specific anti-tumor immunity. We propose that this OV strategy can be applied to MBM to achieve immune cell recruitment, T cell priming, and reversal of T cell exhaustion within the locally infected tumor that simultaneously sustain a distant antitumor immune response.
Methods
To counteract immunosuppressive features of the TME, a third-generation oncolytic adenovirus (Delta-24-RGDOX) has been developed which expresses the immune stimulatory OX40 ligand (OX40L). OX40L is a member of the tumor necrosis factor superfamily receptor, and activation of this pathway is associated with T cell proliferation, activation, and anti-tumor immunity. To explore the ability of Delta-24-RGDOX to achieve oncolysis across a panel of human and murine melanoma cell lines, we quantified its cytotoxic capacity and ability to achieve immunogenic cell death in vitro. Additionally, we used a series of syngeneic murine melanoma models to demonstrate the ability of Delta-24-RGDOX to achieve both local and systemic antitumor immunity. This work included a panel of murine melanoma cell lines which encompass melanoma’s genetic heterogeneity and immunogenicity: B16 3I-F4 (immune checkpoint resistant derivative of B16F10), D4M (BRAFV600E/PTEN-/-, immune checkpoint resistant), and D4M-UV3 (parental D4M with UV induced mutational signature, immunotherapy responsive).
Results
Across the human and murine melanoma cell lines, Delta-24-RGDOX inoculation led to viral infection based on hexon staining and OX40L cell surface expression. Tumor cell cytotoxicity was observed following viral infection as measured by crystal violet assay. Immunogenic cell death was similarly observed. Using our murine models, we demonstrated that Delta-24-RGDOX was able to achieve a significant reduction in tumor size and improved overall survival in B16F10, 3I-F4, D4M, and D4M-UV3 cell lines. The ability to achieve local tumor clearance was similarly observed in orthotopic intracranial models following direct intracranial viral inoculation. We next explored the ability to achieve systemic antitumor immunity in synchronous models of MBM. We demonstrated improvement in overall survival in a model of subcutaneous and intracranial B16F10 where the subcutaneous tumor was treated with Delta-24-RGDOX. In this system, we observed a reduction in bioluminescent imaging of untreated intracranial metastasis following subcutaneous treatment. Lastly, we observed treatment response of untreated intracranial tumors in bilateral intracranial tumors models where a single intracranial tumor was treated with Delta-24-RGDOX.
Conclusion
Delta-24-RGDOX can achieve viral infection, viral oncolysis, and immunogenic cell death following infection of melanoma cell lines. These findings translated in multiple in vivo models including the immunotherapy resistant 3I-F4 and D4M cell lines. Lastly, our preliminary studies suggest that Delta-24-RGDOX can achieve immune cell activation and systemic antitumor immunity against MBM. Future studies are needed to explore the role of T cell priming, recruitment, and clonal expansion in addition to remodeling of the locally infected and distant melanoma TME.