Abstract
The response rates of PD-1/PD-L1 blockade in cancer immunotherapy are relatively low, necessitating the development of novel immune checkpoint inhibitors. Compared with other immune checkpoints, VISTA interacts with its ligand PSGL-1 only under acidic conditions in the tumor microenvironment to suppress the function of CD8+ T cells. On the other hand, drug repurposing offers advantages such as time efficiency and high safety. However, the development of VISTA/PSGL-1 inhibitor based on drug repurposing is still infancy. Here, by screening a library of marketed drugs, we identified Chidamide had a strong binding affinity toward VISTA (KD = 5 nM) and blocked VISTA/PSGL-1 under acidic conditions, thereby significantly enhancing the function of CD8+ T cells and inhibiting the tumor growth in immunocompetent murine CT26 tumor model. This study represents the first discovery of Chidamide as VISTA/PSGL-1 blocker for cancer immunotherapy.