Neddylation inhibition upregulates PD‐L1 expression and enhances the efficacy of immune checkpoint blockade in glioblastoma

Pevonedistat (MLN4924), a specific NEDD8‐activating enzyme inhibitor, has been considered as a promising treatment for glioblastoma, which is currently in Phase I/II clinical trials. On the other hand, inhibition of neddylation pathway substantially upregulates the expression of T cell negative regulator programmed death‐ligand 1 (PD‐L1), which might account for the potential resistance via evasion of immune surveillance checkpoints. Whether administration of anti‐PD‐L1 enhances the efficacy of pevonedistat through a cytotoxic T cell‐dependent mechanism in glioblastoma needs to be investigated. Here, we report that depletion of neddylation pathway key enzymes markedly elevates PD‐L1 expression in glioblastoma cancer cells. Consistently, neddylation inhibitor pevonedistat significantly enhances PD‐L1 expression in both glioblastoma cancer cell lines and animal models. Mechanistically, pevonedistat increases PD‐L1 mRNA levels mainly through inhibiting Cullin1‐F‐box and WD repeat domain‐containing 7 E3 ligase activity and accumulating c‐MYC proteins, a direct transcriptional activator of PD‐L1 gene expression. In addition, inhibition of Cullin3 activity by pevonedistat also blocks PD‐L1 protein degradation. Importantly, pevonedistat attenuates T cell killing through PD‐L1 induction, and blockade of PD‐L1 restores the sensitivity of pevonedistat‐treated glioblastoma cancer cells to T cell killing. The combination of pevonedistat and anti‐PD‐L1 therapy compared to each agent alone significantly increased the therapeutic efficacy in vivo . Our study demonstrates inhibition of neddylation pathway suppresses cancer‐associated immunity and provides solid evidence to support the combination of pevonedistat and PD‐L1/programmed cell death protein 1 immune checkpoint blockade as a potential therapeutic strategy to treat glioblastoma.