Influence of the vaccinating density of A549 cells on tumorigenesis and distant organ metastasis in a lung cancer mice model

Lung metastasis of malignant tumors, such as lung carcinoma, is a major cause of cancer-related deaths worldwide. The commonly used lung tumor models were established by subcutaneous or intravenous injection of the non-small cell lung cancer cell line A549 in mice. However, the influence of cell densities on tumorigenesis and distant organ metastasis remains poorly investigated. In this study, A549 cells were subcutaneously injected into mice at 1 × 107 cells/mL, 5 × 106 cells/mL, and 1 × 106 cells/mL or intravenously at 1 × 106 cells/mL, 5 × 106 cells/mL, and 1 × 106 cells/mL. Then, histology analysis, immunohistochemistry staining, and in-situ TUNEL assay were performed to evaluate tumor growth and metastasis. Results showed that subcutaneously injecting the A549 cells could develop tumors and that fewer apoptotic cells were found in the 5 × 106 cells/mL group than in the other two groups. In groups intravenously injected with A549 cells, there were tumor nodules in all groups, and the 1 × 105 cells/mL group showed longer survival time than the other two groups without any distant organ metastasis. There were tumor nodules formed in the liver in the 1 × 106 cells/mL group at 14 d. Together, our results demonstrated that 5 × 106 cells/mL and 1 × 105 cells/mL are the optimal cell concentrations for the subcutaneous and experimental metastatic models, respectively.