INTRODUCTION: Cancer stem-like cells are thought to be one of the causes of cancer initiation and progression. They are associated with the resistance to radiotherapy and chemotherapy for various types of tumor including esophageal squamous cell carcinoma (ESCC). Therefore, cancer stem-like cells are promising therapeutic targets of cancer. Suppressor of cytokine signaling-1 (SOCS-1) was identified as a negative regulator of various cytokine signaling. We have previously demonstrated that overexpression of SOCS-1 showed a potent anti-tumor effect on ESCC through inhibiting of the JAK/STAT signaling pathway. This study aimed to evaluate the anti-tumor effect of SOCS-1 gene therapy using adenoviral vector (AdSOCS-1) against cancer stem-like cells in ESCC.

METHODS: ESCC cell lines were separated into aldehyde dehydrogenase (ALDH) positive and ALDH negative cells by ALDEFLOUR, and then sphere formation assays were performed. The inhibitory effects of AdSOCS-1 and AdLacZ on the sphere formation were evaluated using TE8, TE14 ESCC cell lines. The inhibition of sphere formation was also evaluated using ESCC cells obtained from ESCC PDX mice (ESCC8). Next, the expression of transcription factors associated with cancer stem-like cells in ESCC was evaluated by RT-PCR. The inhibitory effects on tumor formation by AdSOCS-1 were evaluated by tumorigenicity assay using TE8 xenograft mice.

RESULTS: In the sphere formation assay, ALDH positive TE8 cells and TE14 cells represented strong sphere formation capacity. Compared with AdLacZ infected ALDH positive cells, sphere formation of AdSOCS-1 infected ALDH positive cells was significantly inhibited. The inhibition of sphere formation was also confirmed in ESCC cells obtained from ESCC8 PDX mouse tumor tissue. Interestingly, the expression level of Sox2, a critical stem cell factor regulated by STAT3, was also decreased by AdSOCS-1. Furthermore, AdSOCS-1 decreased the tumorigenic activity of the ALDH positive ESCC tumor cells. CONCLUSIONS: A potent anti-tumor effect of SOCS-1 gene therapy on ESCC may be partially explained by inhibiting the expression of a STAT3 regulated transcription factor critical for cancer stem-like cells.

Citation Format: Ayumi Yamamoto, Eri Munekage, Satoshi Serada, Shigehiro Tsujii, Kosuke Hiramatsu, Minoru Fujimoto, Kazuhiro Hanazaki, Tetsuji Naka. Inhibition of cancer stem-like cells in esophageal squamous cell carcinoma with SOCS-1 gene therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5309.