Inhibition of FOXM1 by thiostrepton sensitizes medulloblastoma to the effects of chemotherapy

Abstract

Medulloblastoma (MB) is the most common malignant brain tumor in children and is highly invasive and metastatic. Despite recent advances, most MB patients suffer significant therapy-related morbidity, and the survival rate for patients with metastatic MB remains unsatisfactory. Altered expression of FOXM1 has been detected in many types of cancers, and the inhibition of FOXM1 has been studied as a cancer therapy. In the present study, we evaluated the impact of the inhibition of FOXM1 by thiostrepton in Daoy MB cells. Cells were treated with different concentrations of thiostrepton alone or in combination with cisplatin. Cell viability was measured with CCK-8 assays, and cell cycle distribution and apoptosis were assessed by flow cytometric analysis. Changes in protein expression were examined by western blotting. RNAi experiments were performed using siRNA oligonucleotides. The invasion and migration studies were performed using 8-µm Transwell plates. Inhibition of FOXM1 by thiostrepton significantly decreased MB cell proliferation. Cell arrest at the G2/M phase and apoptosis were significantly increased in MB cell lines that were treated with thiostrepton or transfected with siRNA. Thiostrepton decreased the IC50 value of cisplatin for MB treatment by enhancing cisplatin-induced apoptosis. Thiostrepton also decreased cell invasion and migration, which are crucial steps for tumor progression. Our data suggest that targeting FOXM1 with small-molecule inhibitors results in potent antitumor activity and chemosensitizing effects in human medulloblastoma cells.