Lung Adenocarcinoma Mouse Models Based on Orthotopic Transplantation of Syngeneic Tumor-Initiating Cells Expressing EpCAM, SCA-1, and Ly6d.

Simple Summary Lung cancer is the leading cause of cancer deaths worldwide and lung adenocarcinoma (LUAD) is the most common type of lung cancer. To better understand the relation between genetic alterations and the characteristics of lung cancer as well as the interactions between tumor cells and components of the tumor microenvironment, we have developed organoid-based orthotopic and syngeneic mouse models of LUAD driven by the KRAS(G12V) or EML4-ALK oncogene. These models formed tumors closely recapitulating the pathology of human LUAD and proved useful tools for in vitro and in vivo drug efficacy studies. In addition, with the use of these models, we identified Ly6d as a potential novel cancer stem cell marker for LUAD. Given their clinical relevance, our mouse models are important tools for studying cancer stem cell biology and LUAD drug development. Somatic mutations in EGFR and KRAS as well as chromosome rearrangements affecting ALK, ROS1, and RET have been identified in human lung adenocarcinoma (LUAD). We here developed organoid-based orthotopic and syngeneic mouse models for studies of the pathogenesis and treatment of LUAD. We isolated EpCAM-positive epithelial cells from mouse lungs and cultured them as organoids to maintain epithelial stem cell properties. These cells were transformed by KRAS(G12V) or EML4-ALK and then transplanted via the trachea into the lungs of the syngeneic mice, where they formed tumors that expressed the lung lineage marker TTF-1 and which closely recapitulated the pathology of human LUAD. Treatment with crizotinib suppressed the growth of tumors formed by the EML4-ALK-expressing lung epithelial cells in a subcutaneous transplantation model. Organoid culture of normal lung epithelial cells resulted in enrichment of EpCAM(+)SCA-1(Ly6a)(+) cells as well as in that of cells expressing another member of the Ly6 protein family, Ly6d, which was found to be required for the growth of the LUAD-initiating cells expressing KRAS(G12V) or EML4-ALK. We also found that a high expression level of LY6D was associated with poor prognosis in human LUAD. Our results thus suggest that LY6D is a potential lung cancer stem cell marker.