MLN4924 is a first-in-class small molecule inhibitor of NEDD8-activating enzyme (NAE), which is currently in several clinical trials for anti-cancer applications. However, MLN4924 also showed some off-target effects with potential to promote the growth of cancer cells which counteracts its anticancer activity. In this study, we found that MLN4924 increases the levels of PD-L1 mRNA and protein in dose- and time-dependent manners. Mechanistic study showed that this MLN4924 effect is largely independent of neddylation inactivation, but is due to activation of both ERK and JNK signals, leading to AP-1 activation, which is blocked by the small molecule inhibitors of MEK and JNK, respectively. Biologically, MLN4924 attenuates T cell killing in a co-culture model due to PD-L1 upregulation, which can be, at least in part, abrogated by either MEK inhibitor or anti-PD-L1 antibody. In an in vivo BALB/c mouse xenograft tumor model, while MLN4924 alone had no effect, combination with either MEK inhibitor or anti-PD-L1 antibody enhanced the suppression of tumor growth. Taken together, our study provides a sound rationale for effective anticancer therapy in combination of anti-PD-L1 antibody or MEK inhibitor with MLN4924 to overcome the side-effect of immunosuppression by MLN4924 via PD-L1 induction.

MLN4924 是一流的 NEDD8 激活酶 (NAE) 小分子抑制剂，目前正在进行多项抗癌应用的临床试验。然而，MLN4924 也显示出一些脱靶效应，可能会促进癌细胞的生长，从而抵消其抗癌活性。在这项研究中，我们发现 MLN4924 以剂量和时间依赖的方式增加 PD-L1 mRNA 和蛋白质的水平。机理研究表明，这种 MLN4924 效应在很大程度上与 neddylation 失活无关，而是由于 ERK 和 JNK 信号的激活，导致 AP-1 激活，这分别被 MEK 和 JNK 的小分子抑制剂阻断。在生物学上，由于 PD-L1 上调，MLN4924 减弱了共培养模型中的 T 细胞杀伤，至少部分是，被 MEK 抑制剂或抗 PD-L1 抗体废除。在体内 BALB/c 小鼠异种移植肿瘤模型中，虽然单独使用 MLN4924 没有效果，但与 MEK 抑制剂或抗 PD-L1 抗体联合使用可增强对肿瘤生长的抑制。综上所述，我们的研究为将抗 PD-L1 抗体或 MEK 抑制剂与 MLN4924 联合使用以克服 MLN4924 免疫抑制的副作用提供了有效的抗癌疗法的合理依据通过PD-L1 诱导。