Abstract
PURPOSE: Radiotherapy is a major treatment method for patients with non-small cell lung cancer (NSCLC). However, the presence of radioresistant cancer stem cells (CSCs) may be associated with disease relapse or a poor outcome after radiotherapy. Voltage-gated calcium channel α2δ1 subunit (encoded by the gene CACNA2D1) isoform 5 is a marker of CSCs in hepatocellular carcinoma. This study aimed to investigate the radiosensitivity of α2δ1-high cells in NSCLC cell lines. MATERIALS AND METHODS: NSCLC cell lines A549, H1975, H1299, and PC9 were used. CACNA2D1-knockdown and CACNA2D1-overexpressing cell lines were established by lentiviral infection. Colony formation assay was performed to determine radiosensitivity. Sphere formation assay in serum-free medium was performed to evaluate self-renewal capacity. Proteins associated with DNA damage repair were analyzed by immunofluorescence or Western blot. The monoclonal antibody of α2δ1 was applied alone or in combination with radiation either in vitro or in vivo to determine the anti-tumor effect of the antibody. RESULTS: α2δ1-high cells showed greater sphere-forming efficiency than α2δ1-low cells and were relatively resistant to radiation. CACNA2D1 knockdown in A549 cells enhanced radiosensitivity, whereas CACNA2D1 overexpression in PC9 and H1975 cells reduced radiosensitivity, suggesting that α2δ1 imparted radioresistance to NSCLC cells. Analysis of proteins involved in DNA damage repair suggested that α2δ1 enhanced the efficiency of DNA damage repair. The monoclonal antibody of α2δ1 had a synergistic effect with that of radiation to block the self-renewal of α2δ1-high cells and enhanced the radiosensitivity of α2δ1-positive cells in colony formation assays. The combination of the α2δ1 antibody with radiation repressed A549 xenograft growth in vivo. CONCLUSION: α2δ1 enhances radioresistance in cancer stem-like cells in NSCLC. The α2δ1 monoclonal antibody sensitizes α2δ1-high cells to radiation, suggesting that the antibody may be used to improve the treatment outcome when combined with radiation in NSCLC.