Dual inhibition of MEK and AXL targets tumor cell heterogeneity and prevents resistant outgrowth mediated by the epithelial-to-mesenchymal transition in NSCLC.

The epithelial-to-mesenchymal transition (EMT) is a dynamic epigenetic reprogramming event that occurs in a subset of tumor cells and is an initiating step towards invasion and distant metastasis. The process is reversible and gives plasticity to cancer cells to survive under variable conditions, with the acquisition of cancer stem cell-like characteristics and features such as drug resistance. Therefore, understanding survival dependencies of cells along the phenotypic spectrum of EMT will provide better strategies to target the spatial and temporal heterogeneity of tumors and prevent their ability to bypass single inhibitor treatment strategies. To address this, we integrated the data from a selective drug screen in epithelial and mesenchymal Kras/p53 (KP) mutant lung tumor cells with separate datasets including reverse phase protein array and an in vivo shRNA dropout screen. These orthogonal approaches identified AXL and MEK as potential mesenchymal and epithelial cell survival dependencies, respectively. To capture the dynamicity of EMT, incorporation of a dual fluorescence EMT sensor system into murine KP lung cancer models enabled real time analysis of the epigenetic state of tumor cells and assessment of the efficacy of single agent or combination treatment with AXL and MEK inhibitors. Both 2-D and 3-D culture systems and in vivo models revealed that this combination treatment strategy of MEK plus AXL inhibition synergistically killed lung cancer cells by specifically targeting each phenotypic subpopulation. In conclusion, these results indicate that co-targeting the specific vulnerabilities of EMT subpopulations can prevent EMT-mediated drug resistance, effectively controlling tumor cell growth and metastasis.