Mitomycin C enhanced the efficacy of PD-L1 blockade in non-small cell lung cancer

Programmed death ligand 1 (PD-L1) immune checkpoint inhibitors are promising therapeutic agents for treating cancers but the response rate is <20%. Some chemotherapeutic drugs could also activate an anticancer immune response to kill cancer cells, apart from their direct cytotoxicity. Our study investigated the combination of chemotherapeutic drugs with PD-L1 antibody to enhance the response rate of PD-L1 blockade. Non-small cell lung cancer (NSCLC) cells were pre-treated with mitomycin C (MMC) and then co-cultured with peripheral blood mononuclear cells (PBMCs) to investigate the effect of the combination of MMC with PD-L1 antibody. The drug combination was also evaluated in vivo in Lewis lung cancer (LLC) cells-bearing C57BL/6 mice. MMC increased the expressions of PD-L1 and MHC-I in NSCLC cells in vitro and in vivo and enhanced the cytotoxic effect of lymphocytes on NSCLC in vitro. In LLC-bearing mouse model, the combination of MMC and PD-L1 antibody was found to be more effective in retarding tumor growth and prolonging overall survival than either single treatment alone, which was associated with increased lymphocyte infiltration and granzyme B release. Mechanistically, MMC activated the ERK pathway, which subsequently enhanced the binding of c-JUN to the PD-L1 promoter and recruited its co-factor STAT3 to increase PD-L1 expression. The upregulated ERK pathway was shown to activate p65 to increase the MHC-I expression. MMC was shown to enhance the efficacy of PD-L1 blockade in NSCLC cells. Further study is warranted to translate the findings to clinical application.