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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.

Objects: Cyclooxygenase-2 (COX-2), the enzyme that converts arachidonic acid to prostaglandins, is overexpressed in a variety of tumors, including medulloblastoma (MB). CD133, a transmembrane glycoprotein, has been suggested as a marker for cancer stem cells in brain tumors. The aim of the present study was to investigate the role of celecoxib, a selective COX-2 inhibitor, in enhancing the effects of ionizing radiotherapy (IR) on medulloblastoma-derived CD133-positive cells (MB-CD133(+))., Materials and Methods: MB-CD133(+) were isolated from two medulloblastoma cell lines (Daoy and UW228). Then, they were treated with celecoxib in different concentrations, and cell viability was assessed. The assays of cell survival, soft agar, radiosensitivity, colony formation, and apoptotic activity in MB-CD133(+) treated with celecoxib alone, radiation alone, or celecoxib combined with radiation were further evaluated., Results: MB-CD133(+) showed the self-renew ability to form sphere bodies in vitro and regenerate tumors in vivo. The levels of COX-2 mRNA and protein in MB-CD133(+) were significantly higher than those in MB-CD133(-). The treatment of 30 μM celecoxib could effectively inhibit the abilities of cell proliferation and colony formation and increase IR-induced apoptosis in treated MB-CD133(+). Furthermore, in vivo study demonstrated that celecoxib significantly enhanced radiosensitivity in MB-CD133(+)-transplanted grafts. Notably, xenotransplantation analysis demonstrated that the treatment of celecoxib could further suppress the expressions of angiogenic and stemness-related genes in treated MB-CD133(+) grafts of SCID mice., Conclusions: Celecoxib presents the potential of radiosensitizing effect in MB-derived cancer stem cells. Therefore, it should be warranted in future trials to enhance the radiotherapeutic effects in MB patients.