Thioridazine Sensitizes Esophageal Carcinoma Cell Lines to Radiotherapy-Induced Apoptosis In Vitro and In Vivo

BACKGROUND Radiotherapy is one of the primary treatments for esophageal squamous cell carcinoma (ESCC). Identification of novel radio-sensitizing agents will improve the therapeutic outcome of radiotherapy. This study aimed to determine the radio-sensitizing effect of the antipsychotic agent thioridazine in ESCC and explored the underlying mechanisms. MATERIAL AND METHODS ECA-109 and TE-1 ESCC cells were treated with thioridazine and radiotherapy alone and in combination. Cell survival was measured by MTT assay. Cell cycle and apoptosis were monitored by flow cytometry. Western blot analysis was used to analyze the expression of phospho-PI3K, phosphor-AKT, phospho-mTOR, Caspase-3, Caspase-9, Bax, Bcl-2, Bal-xl, Bak, and p53. The xenograft mouse model was used to study the in vivo anticancer effect of thioridazine and irradiation. RESULTS Combined treatment with thioridazine and irradiation significantly reduced viability of ESCC cells compared with thioridazine or irradiation treatment alone. Thioridazine and irradiation treatment induced G0/G1 phases cell cycle arrest through down-regulation of CDK4 and cyclinD1. In addition, thioridazine and irradiation treatment induced apoptosis through up-regulation of cleaved capase-3 and 9, as well as an increase in the expression of Bax and Bak and a decrease in the expression of Bcl-2 and Bcl-xl. Furthermore, thioridazine and irradiation treatment inhibited the PI3K-AKT-mTOR pathway and up-regulated the expression of p53. In xenograft mice, thioridazine and irradiation reduced ESCC tumor growth. CONCLUSIONS Thioridazine sensitizes ESCC cells to radiotherapy. Thioridazine may play a role in ESCC radiation therapy as a promising radiosensitizer.