Aldehyde Dehydrogenase 1A1 Possesses Stem-Like Properties and Predicts Lung Cancer Patient Outcome

Introduction: Lung cancer contains a small population of cancer stem cells that contribute to its initiation and progression. We investigated the biological function and clinical significance of aldehyde dehydrogenase 1A1 (ALDH1A1) in non-small-cell lung carcinoma (NSCLC). Methods: ALDH1A1 assay or small interfering RNA transfection was employed to isolate ALDH1A1+ cells or knock down ALDH1A1 expression in H2087 cells, respectively. Biological functions of ALDH1A1+ and ALDH1A1 silenced cells were investigated using in vitro and in vivo methods. ALDH1A1 expression was analyzed using immunohistochemistry on tissue microarrays with 179 lung cancer tissues and 26 normal lung tissues. Results: The abilities of clone formation, proliferation, cell growth, and migration were increased in ALDH1A1+ and ALDH1A1 silenced cells. ALDH1A1+ lung cancer cells initiated tumors that resembled the histopathologic characteristics and heterogeneity of the parental lung cancer cells in mice. The silencing of ALDH1A1 expression in H2087 lung cancer cells inhibited cell proliferation and migration significantly. ALDH1A1 was expressed in 42% of normal lung tissues (11 of 26), with strong expression in the basal cells and globular cells of the normal bronchus and weak expression in the alveolar epithelial cells. Compared with normal lung tissues, 45% of NSCLC samples (81 of 179) were read as positive for ALDH1A1. Positive ALDH1A1 expression was correlated with patients' smoking status (p = 0.022), lymph-node metastasis (p = 0.006), clinical stage (p = 0.004), and a decreased overall survival time (p < 0.001). Positive ALDH1A1 expression in lung cancer tissues was an independent prognostic factor for NSCLC (odds ratio = 5.232, p < 0.001). Conclusion: Elucidating the biological functions of ALDH1A1 could be helpful in studying lung tumorigenesis and for developing new therapeutic approaches.