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.