Triple blockade of EGFR, MEK and PD-L1 has antitumor activity in colorectal cancer models with constitutive activation of MAPK signaling and PD-L1 overexpression

S Napolitano,A L Muddassir,S Kopetz,D Ciardiello,E F Giunta,V De Falco,M Furia,T Troiani,N Matrone,V Belli,F Morgillo,G Martini,A Sorokin,F Ciardiello,E Martinelli

doi:10.1186/s13046-019-1497-0

Abstract

BackgroundMolecular 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.MethodsWe have generated in vitro and in vivo different CRC models in order to underline the mechanisms of MEKi resistance.ResultsThe 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.ConclusionsThese 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.

Highlights

Molecular mechanisms driving acquired resistance to anti-epidermal growth Factor receptor (EGFR) therapies in metastatic colorectal cancer are complex but generally involve the activation of the downstream RAS-RAF-MEK-MAPK pathway
MEK inhibitor (MEKi) display a CMS4 gene expression profile In previous works, we have demonstrated that MEK is a key downstream effector of EGFR pathway that must be inhibit to prevent and/or delay the onset of acquired resistance to anti-EGFR treatment [3, 10, 11, 18,19,20,21]
We have found that some tumors after an initial benefit to MEKi treatment, started to regrowth limiting its use [11]

Summary

Introduction

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. The epidermal growth Factor receptor (EGFR) family plays a key role in tumor growth and progression by promoting a variety of functions including proliferation, survival, invasion, and immune evasion [2] These therapies have improved patient responses, despite significant progress in strategies for cancer treatment, their use is limited by the presence of pre-existing intrinsic resistance mechanisms or by the ability of cancer cells to acquire resistance [3, 4, 6]. We recently have demonstrated that the plethora of alterations that emerge at progression from treatment with the antiEGFR moAb cetuximab, biochemically converge to reactivate the main EGFR downstream effector, the RASRAF-MEK-MAPK pathway [3, 10] Based on this hypothesis, we have evaluated the ability of selective MEK inhibitors (MEKi) in overcoming cetuximab resistance in various human CRC models [10]. To identify possible mechanisms of resistance we have generated and characterized different in vitro and in vivo MEKi-resistant colon cancer models

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Conclusion