Irradiation Enhances the Tumor Tropism and Therapeutic Potential of Tumor Necrosis Factor‐Related Apoptosis‐Inducing Ligand‐Secreting Human Umbilical Cord Blood‐Derived Mesenchymal Stem Cells in Glioma Therapy

Irradiation is a standard therapy for gliomas and many other cancers. Tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL) is one of the most promising candidates for cancer gene therapy. Here, we show that tumor irradiation enhances the tumor tropism of human umbilical cord blood‐derived mesenchymal stem cells (UCB‐MSCs) and the therapeutic effect of TRAIL delivered by UCB‐MSCs. The sequential treatment with irradiation followed by TRAIL‐secreting UCB‐MSCs (MSC‐TRAIL) synergistically enhanced apoptosis in either TRAIL‐sensitive or TRAIL‐resistant glioma cells by upregulating the death receptor 5 and by inducing caspase activation. Migration assays showed greater MSC migration toward irradiated glioma cells and the tumor site in glioma‐bearing mice compared with unirradiated tumors. Irradiated glioma cells had increased expression of interleukin‐8 (IL‐8), which leads to the upregulation of the IL‐8 receptor on MSCs. This upregulation, which is involved in the migratory capacity of UCB‐MSCs, was confirmed by siRNA inhibition and an antibody‐neutralizing assay. In vivo survival experiments in orthotopic xenografted mice showed that MSC‐based TRAIL gene delivery to irradiated tumors had greater therapeutic efficacy than a single treatment. These results suggest that clinically relevant tumor irradiation increases the therapeutic efficacy of MSC‐TRAIL by increasing tropism of MSCs and TRAIL‐induced apoptosis, which may be a more useful strategy for cancer gene therapy. STEM CELLS 2010;28:2217–2228