EXTH-33. The oncolytic adenovirus RGDOX sensitizes the anti-tumor efficacy of immune checkpoint blockades in murine melanoma brain metastases models

Amongst solid cancers, melanoma brain metastases (MBM) have the highest likelihood of metastasizing to the brain. The use of immune checkpoint inhibitors (ICI) for metastatic melanoma has emerged as first line therapy; however, intracranial progression and acquired resistance highlight the need for novel immunotherapeutic strategies for this patient population. Oncolytic viral (OV) therapy leverages tumor cell replication machinery to selectively replicate and kill tumor cells while promoting anti-tumor immunity through modulation of the tumor microenvironment (TME). The oncolytic adenovirus Delta-24-RGDOX (RGDOX) has been shown to function as a TME modulator in both preclinical and clinical settings. Here, we investigated the anti-tumor efficacy of RGDOX combined with ICIs in synchronous extracranial and intracranial (s.c.-i.c.) murine melanoma models (B16F10 and D4M). Using this approach, we inoculated the s.c. tumor with Delta-24-RGDOX and monitored for viral induced cytotoxicity within the infected tumor while assessing for the simultaneous generation of intracranial antitumor immunity. The combinatorial strategy of Delta-24-RGDOX with PD-1/CTLA-4 inhibition significantly reduced both infected s.c. and distant i.c. tumor growth while also improving survival in tumor bearing mice. Through a series of immune depletion experiments, therapeutic efficacy was determined to be mediated through CD8+ T cells. Additionally, eradication of subcutaneous tumor led to immunologic memory preventing intracranial tumor formation. Immunophenotyping and spatial profiling approaches, including full-spectrum flow cytometry and COMET multiplex immunofluorescence analysis, demonstrated the combination of RGDOX with ICI boosted anti-tumor immunity in both s.c. and i.c. tumors through enhanced T-cell activity and increased infiltration of dendritic cells and anti-tumor M1 macrophages. In contrast, immunosuppressive populations, such as myeloid-derived suppressor cells and M2 macrophages, were markedly reduced in both s.c. and i.c. tumors in the combination treatment group. These findings suggest the clinical translation of RGDOX with PD-1/CTLA-4 inhibition is a promising therapeutic approach for the generation of antitumor immunity against MBM.