Epigenetic therapy to enhance therapeutic effects of PD-1 inhibition in uveal melanoma

Targeted therapy and immunotherapy have revolutionized the treatment of metastatic skin melanoma but none of the treatments are approved for patients with metastatic uveal melanoma (UM). Here we hypothesized that the poor responses to immunotherapy of UM can be enhanced by epigenetic modulation using HDAC or BET inhibitors (BETi). Cultured uveal melanoma cells were treated with the HDAC inhibitor (HDACi) entinostat or BETi JQ1. Entinostat induced HLA expression and PD-L1, but JQ1 did not. A syngenic mouse model carrying B16-F10 melanoma cells were treated with PD-1 and CTLA-4 inhibitors, which was curative. Co-treatment with the bioavailable BETi iBET-726 impaired the immunotherapy effect. Monotherapy of a B16-F10 mouse model with anti-PD-1 resulted in a moderate therapeutic effect that could be enhanced by entinostat. Mice carrying PD-L1 knockout B16-F10 cells were also sensitive to entinostat. This suggests HDAC inhibition and immunotherapy could work in concert. Indeed, co-cultures of UM with HLA-matched melanoma-specific tumor-infiltrating lymphocytes (TILs) resulted in higher TIL-mediated melanoma killing when entinostat was added. Further exploration of combined immunotherapy and epigenetic therapy in metastatic UM is warranted.