1267 Cimetidine enhances PD-1 blockade efficacy in melanoma by regulating PD-L1 expression on tumor

Although immune checkpoint proteins such as PD-1 and CTLA-4 are important targets to enhance the survival of patients with melanoma, clinical success is not allowed to the most patients with limited responsiveness to these treatments. Cimetidine(CIM), which is one of histamine receptor H2 antagonists, has been reported as having anti-tumor effect to different cancers including melanoma. In this study, we investigated B16 melanoma-bearing mouse treated with CIM and/or a-PD-1. PD-L1 expression on tumor cells is dynamically regulated by the combination treatment of CIM and a-PD-1 and consequently, tumor growth is dramatically suppressed. Based on these results, it is possible that the combination treatment of CIM and a-PD-1 is considered as promising therapeutic strategy for melanoma.