The role of Epithelial to Mesenchymal Transition (EMT)-like process in drug resistance, progression and relapse in Bone Marrow Disease in Neuroblastoma

The presence of neuroblastoma (NB) cells in the bone marrow (BM) portends a poor outcome for some children and may provide a haven for drug-resistant metastatic cells. Interconversion of NB cells between two phenotypes, called adrenergic (ADRN) and mesenchymal (MES), may occur in vitro. While the presence of ADRN tumour cells is well established, the presence of MES NB cells in patients has been controversial. Since MES NB cells are reportedly resistant to chemotherapy, I hypothesised that an Epithelial to Mesenchymal Transition (EMT)-like process drives progression and relapse of NB in the BM in patients with high-risk NB.
I have successfully isolated MES NB cells from BM aspirates of patients, confirming that MES NB cells are not only an in vitro phenomenon. Validation of MES proteins on sequential BM aspirates of patients with high-risk NB using High-Content Imaging, and on paired BM trephines and primary tumours using immunohistochemistry, suggests that periostin and YAP-1/TAZ may be good candidates to detect these cells.
The BM is a hypoxic microenvironment, and I confirmed that hypoxia induced a MES phenotype in SH-SY-5Y cells, which was associated with chemoresistance. Proteomic and RNA data revealed that the hypoxia-induced MES phenotype was sustained following reoxygenation, suggesting that cells were transcriptionally reprogrammed.
I demonstrated that isolated MES NB cells from the BM were chemoresistant, further supporting my hypothesis. These cells were exploited to identify potential targetable pathways in a bespoke in silico drug-repurposing pipeline. Compared to established cell lines, patient-derived cultures are more reflective of patient heterogeneity, highlighting their added value in preclinical studies.
In summary, I have shown that MES NB cells can be identified in the BM of patients and are drug-resistant. Promising candidates to identify MES cells need to be further evaluated, aiming to combine them with the existing NB panel to assess BM disease.