PD-L1 induction via the MEK-JNK-AP1 axis by a neddylation inhibitor promotes cancer-associated immunosuppression

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.