BACKGROUND Molecular mechanisms driving acquired resistance to anti-EGFR therapies in metastatic colorectal cancer (mCRC) are complex but generally involve the activation of the downstream RAS-RAF-MEK-MAPK pathway. Nevertheless, even if inhibition of EGFR and MEK could be a strategy for overcoming anti-EGFR resistance, its use is limited by the development of MEK inhibitor (MEKi) resistance. METHODS We have generated in vitro and in vivo different CRC models in order to underline the mechanisms of MEKi resistance. RESULTS The three different in vitro MEKi resistant models, two generated by human CRC cells quadruple wild type for KRAS, NRAS, BRAF, PI3KCA genes (SW48-MR and LIM1215-MR) and one by human CRC cells harboring KRAS mutation (HCT116-MR) showed features related to the gene signature of colorectal cancer CMS4 with up-regulation of immune pathway as confirmed by microarray and western blot analysis. In particular, the MEKi phenotype was associated with the loss of epithelial features and acquisition of mesenchymal markers and morphology. The change in morphology was accompanied by up-regulation of PD-L1 expression and activation of EGFR and its downstream pathway, independently to RAS mutation status. To extend these in vitro findings, we have obtained mouse colon cancer MC38- and CT26-MEKi resistant syngeneic models (MC38-MR and CT26-MR). Combined treatment with MEKi, EGFR inhibitor (EGFRi) and PD-L1 inhibitor (PD-L1i) resulted in a marked inhibition of tumor growth in both models. CONCLUSIONS These results suggest a strategy to potentially improve the efficacy of MEK inhibition by co-treatment with EGFR and PD-L1 inhibitors via modulation of host immune responses.

中文翻译：

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EGFR，MEK和PD-L1的三重阻断在结直肠癌模型中具有抗肿瘤活性，并具有MAPK信号传导和PD-L1过表达的组成性激活。

背景技术在转移性结直肠癌（mCRC）中驱动获得的对抗EGFR疗法的获得性抗性的分子机制是复杂的，但是通常涉及下游RAS-RAF-MEK-MAPK途径的激活。尽管如此，即使抑制EGFR和MEK可能是克服抗EGFR耐药性的策略，但其使用仍受到MEK抑制剂（MEKi）耐药性发展的限制。方法我们已经在体外和体内生成了不同的CRC模型，以强调MEKi抗性的机制。结果三种不同的体外MEKi抗药性模型，其中两种是由人类CRC细胞针对KRAS，NRAS，BRAF，PI3KCA基因（SW48-MR和LIM1215-MR）和一个带有KRAS突变的人CRC细胞（HCT116-MR）表现出与大肠癌CMS4基因签名相关的特征，免疫途径上调，通过芯片和Western blot证实分析。特别地，MEKi表型与上皮特征的丧失以及间充质标志物和形态的获得有关。形态变化伴随着PD-L1表达的上调和EGFR及其下游途径的激活，而与RAS突变状态无关。为扩展这些体外研究结果，我们获得了小鼠结肠癌MC38-和CT26-MEKi耐药同基因模型（MC38-MR和CT26-MR）。MEKi，EGFR抑制剂（EGFRi）和PD-L1抑制剂（PD-L1i）的联合治疗在两种模型中均显着抑制了肿瘤的生长。