Evaluating The Role Of The Cox2/Pge2 Pathway In Anti-Melanoma Immunity.

e14114 Background: Checkpoint inhibitors such as anti-PD1 (aPD1) have revolutionized treatment of metastatic melanoma. However, a large subset of patients receiving such treatment fails to respond to aPD1 monotherapy due to mechanisms such as PD-L1 upregulation within the tumor and T cell exhaustion in the tumor microenvironment. The PGE2/COX2 signaling pathway is one of the pathways implicated in T cell exhaustion and PD1/PD-L1 upregulation and thus represents an attractive pharmacologic target to enhance effects of aPD1 therapy due to the availability and safety of inhibitors such as aspirin or NSAIDs. There is evidence that PGE2/COX2 pathway inhibitors act synergistically with aPD1 therapy in murine melanoma and breast cancer models. Here we aimed to further characterize this synergism using the YUMMER (Yale University Mouse Melanoma Exposed to Radiation) 1.7 model, an irradiated, syngeneic cell line originating from BrafV600E; Pten-/-; and Cdkn2a -/- genetically engineered mouse melanomas. YUMMER1.7 cells implanted into the flanks of C57BL6/j mice show reproducible but partial responses to intraperitoneal aPD1 therapy and thus serves as an ideal platform to study whether concurrent PGE2/COX2 pathway blockade may result in additive effects to aPD1 therapy. Methods: 6-7 week old male C57BL6/j mice (n = 20) were injected with 500K YUMMER1.7 cells and treated with aPD1 therapy alone starting on day 7 after tumor implantation (n = 10) or with aPD1 therapy starting on day 7 in addition to ibuprofen dissolved in drinking water at a concentration of 1 mg/mL started on the day of tumor implantation (n = 10). Using an average daily water consumption estimate of 6 mL/day, this translates to a human equivalent of roughly 1200 mg/day, a moderate dose of ibuprofen. Tumor growth was monitored and tracked to an endpoint of 1cm3. Results: Tumor volume at day 17 significantly differed between the two groups (p < 0.0001). Survival curves were significantly different between the two groups (p < 0.0001); all tumors treated with aPD1 alone grew to endpoint by day 32, while all tumors treated with aPD1 + ibuprofen regressed with 8 out of 10 showing complete regression by day 32. Conclusions: We have shown that ibuprofen strongly synergizes with aPD1 therapy in a murine model of melanoma, complementing existing evidence. This suggests that PGE2/COX2 inhibitors such as NSAIDs, which are over-the-counter agents with a well-studied safety profile, may serve as a promising means of enhancing the response to aPD1 therapies such as nivolumab in melanoma patients who initially fail aPD1 monotherapy.