MEK inhibition overcomes chemoimmunotherapy resistance by inducing CXCL10 in cancer cells [LLC1]

Chemotherapy with anti PD-1/PD-L1 mAb has become the standard of care for patients with metastatic non-small cell lung cancer (NSCLC). Using lung tumor models, where pemetrexed-platinum chemotherapy (PEM/CDDP) remains unable to synergize with immune checkpoint inhibitors (ICI), we linked failure of this treatment with its inability to induce CXCL10 expression and CD8+ T cell recruitment. Using drug screening, we showed that combining a MEK inhibitor (MEKi) with PEM/CDDP triggers CXCL10 secretion by cancer cells and CD8+ T cell recruitment, and restores ICI efficacy. PEM/CDDP plus MEKi promotes optineurin (OPTN)-dependent mitophagy, resulting in CXCL10 production in a mitochondrial DNA and TLR9-dependent manner. TLR9 or autophagy/mitophagy processes genetic inactivation of abort the antitumor efficacy of PEM/CDDP plus MEKi/anti PD-L1 therapy. In human NSCLC, high OPTN, TLR9 and CXCL10 expression is associated with better response to ICI. Our results underline the role of TLR9 and OPTN-dependent mitophagy in enhancing chemoimmunotherapy efficacy. All conditions are in triplicat and analyszed at two times after treatment (6 (T6) and 24hrs (T24)). Control LLC1 cells (NT) were treated only with 0,1% DMSO. CP cells were treated with cisplatin (2.5µM) and pemetrexed (2.5 µM). T cells were treated with trametinib (MEK inhibiteur, 10 nM). TCP cells were treated with both cisplatin, pemetrexed and trametinib. Total RNA from tumor cells was extracted with TriReagent (Fisher Scientific), RNA Sequencing was performed by the GenomEast platform, a member of the “France Génomique” consortium (ANR-10-INBS- 0009). Differential expression analysis was performed with the DESeq2 R package (Love et al., 2014). LLC1 cells treated with trametinib, PEM/CDDP or PEM/CDDP plus trametinib were compared to each other and to the control group. Raw p-values associated with each gene were adjusted using Bonferroni correction, as advised. For each comparison, genes with an-adjusted p-value < 0.10 were selected as differential.