Introduction. Treatment of chemoresistant or refractory, bone-marrow metastatic neuroblastoma remains a major challenge. The substantial fraction of patients who fail induction chemotherapy can be considered ultra-high risk and require novel treatments targeted at the actionable genetic changes associated with development of chemorefractory disease and bone-marrow metastasis. The lack of any in vivo models that are immunocompetent and natively recapitulate ultra-high risk disease and spontaneous bone-marrow metastasis has impeded experimental focus in this critical area.
Results. We subjected the well-characterised Th-MYCN genetically-engineered mouse (GEM) model, which is largely chemosensitive and free of metastasis at tumour onset, to multicycle induction chemotherapy protocols. Th-MYCNR mice develop primary tumours that are fully chemorefractory and metastatic to bone-marrow. Explants and primary cell cultures derived from Th-MYCNR primary tumours retain treatment resistance in subcutaneous and intratibial re-implantation, indicating that the growth advantage attributed to chemoresistance is cell-intrinsic. Gene expression analysis of primary resistant tumours reveals changes in PI3K-AKT, MAPK and RAS pathways. Misregulation of “extracellular matrix receptor (ECM) interaction” and β-catenin pathways reveals a signature consistent with epithelial-mesenchymal transition (EMT). In support of this finding, immunohistochemical analysis showed increased staining of ECM and mesenchymal markers in relapsed tumours compared to untreated tumours.
Discussion. Here we report the first native, unmanipulated neuroblastoma model that recapitulates treatment induction failure and widespread disease metastasis in an immunocompetent setting. Th-MYCNR reveals critical changes associated with development of treatment resistance and metastasis, such as altered expression of actionable pathways, and a potential EMT state change in metastasis. Th-MYCNR will be a powerful experimental tool for molecular dissection of clonal evolution that drives development of treatment resistance and metastasis in neuroblastoma.