Inhibition of phosphorylated STAT3 by cucurbitacin I enhances chemoradiosensitivity in medulloblastoma-derived cancer stem cells

Introduction: CD133 (PROM1) is a potential marker for cancer stem cells (CSCs), including those found in brain tumors. Recently, medulloblastoma (MB)-derived CD133-positive cells were found to have CSC-like properties and were proposed to be important contributors to tumorigenicity, cancer progression, and chemoradioresistance. However, the biomolecular pathways and therapeutic targets specific to MB-derived CSCs remain unresolved. Materials and methods: In the present study, we isolated CD133⁺ cells from MB cell lines and determined that they showed increased tumorigenicity, radioresistance, and higher expression of both embryonic stem cell-related and drug resistance-related genes compared to CD133^- cells. Bioinformatics analysis suggested that the STAT3 pathway might be important in MB and CD133⁺ cells. To evaluate the effects of inhibiting the STAT3 pathway, MB-derived CD133^+/- cells were treated with the potent STAT3 inhibitor, cucurbitacin I. Treatment with cucurbitacin I significantly suppressed the CSC-like properties and stemness gene signature of MB-derived CD133⁺ cells. Furthermore, cucurbitacin I treatment increased the apoptotic sensitivity of MB-derived CD133⁺ cells to radiation and chemotherapeutic drugs. Notably, cucurbitacin I demonstrated synergistic effects with ionizing radiation to inhibit tumorigenicity in MB-CD133 ⁺-inoculated mice. Results: These results indicate that the STAT3 pathway plays a key role in mediating CSC properties in MB-derived CD133 ⁺ cells. Targeting STAT3 with cucurbitacin I may therefore represent a novel therapeutic approach for treating malignant brain tumors.