Abstract: Objective To investigate the mechanism mediating the inhibitory effect of chidamide on esophageal squamous cell carcinoma (ESCC) cells. Methods ESCC cell lines KYSE-150, KYSE-450 and KYSE-510 were treated with 5, 10, 20, or 40 μmol/L of chidamide, and the changes in cell proliferation, colony-forming capacity, cell apoptosis and cell cycle were assessed using MTT aasay, colony formation experiment and flow cytometry. Western blotting was performed to detect the expression levels of cleaved caspase-3, cleaved PARP, p21, cyclin D1, p-Akt, p-ERK1/2, γH2AX, H3K9ac, and Ki-67. In a nude mouse model bearing subcutaneous ESCC xenografts, the effects of intraperitoneal injection of 20 mg/kg chidamide for 3 days on tumor size and body weight were observed every 3 days, and Ki-67 and CD31 expressions in the tumor tissues were detected using immunohistochemistry. Tubular formation experiment was used to examine the effect of chidamide on tubular formation of human umbilical vein endothelial cells (HUVECs) in vitro. Results In cultured ESCC cell lines, chidamide significantly inhibited cell proliferation and colony formation (P<0.05), promoted cell apoptosis, and increased the percentage of G0/G1 phase cells (all P<0.01). Chidamide obviously up- regulated cleaved caspase-3, cleaved PARP, p21, γH2AX, and H3K9ac and down-regulated cyclin D1, p-Akt and p-ERK1/2, and Ki-67 in the cells (P<0.01). In the tumor-bearing mouse models, treatment with chidamide significantly reduced the tumor volume (P<0.05), tumor to body weight ratio (P<0.01), and the expression levels of Ki-67 and CD31 in the tumors (P<0.01). Chidamide also significantly inhibited tubule formation in cultured HUVECs (P<0.05). Conclusion Chidamide inhibits proliferation, induces apoptosis and blocks cell cycle of ESCC cells possibly by inhibiting the PI3K/Akt and ERK1/2 pathways and increasing DNA damage. Chidamide also inhibits subcutaneous tumorigenesis of ESCC cells in mice by inhibiting tumor cell proliferation and angiogenesis.

Key words: chidamide; esophageal squamous cell carcinoma; proliferation; apoptosis; cell cycle