A novel immunocompetent mouse model of neuroblastoma bone marrow metastasis as a therapeutic target for mesenchymal stem cell-based immunotherapy.

BACKGROUND: Recent advances in immunotherapy have highlighted the need for clinically relevant immunocompetent models of metastatic neuroblastoma. However, such models of bone marrow (BM) metastasis remain limited. We previously developed a gene-modified mesenchymal stem cell (MSC)-based immunotherapeutic strategy that functions as a tumor-selective drug delivery system (DDS) and demonstrated its antitumor efficacy in a localized TH-MYCN neuroblastoma model. Therefore, this study aimed to establish a reproducible immunocompetent mouse model of neuroblastoma BM metastasis as a platform for evaluating novel therapeutic strategies. METHODS: Primary cultured tumor cells derived from spontaneous tumors of homozygous TH-MYCN mice were intravenously injected (1×107 cells) into the orbital venous plexus of wild-type mice. BM metastasis was assessed 21 days after injection using spinal immunohistochemistry and ex vivo culture of femur-derived bone marrow cells with GD2 expression analysis by flow cytometry. A separate cohort of 17 mice were monitored for survival. MSC biodistribution was evaluated after intraperitoneal administration of DiR-labeled or copGFP-transduced MSCs using an in vivo imaging system (IVIS) and immunohistochemistry. RESULTS: BM metastases were detected in 6 of 9 mice (66.7%). Twelve of the 17 mice died at 17-74 days (median, 29 days) after injection. Mice with BM metastasis developed significant anemia compared with controls. IVIS and immunohistochemical analyses demonstrated MSC accumulation in spinal BM lesions. CONCLUSION: We established a clinically relevant immunocompetent neuroblastoma BM metastasis model and demonstrated MSC homing to metastatic BM lesions, providing a useful platform for evaluating therapies targeting metastatic neuroblastoma.