CSN5-IN-1 (compound Ac-11) is an inhibitor of CSN5 , with IC 50 values of 12.56 μM and 19 μM as measured by FP assay and fluorescence assay, respectively. CSN5-IN-1 can also downregulate the expression of PD-L1 and upregulate the expression of NEDD8-Cul1 in cells.