Purpose
Neuroblastoma (NB) cells in the bone marrow are a hallmark of high-risk disease, selecting children for more intensive treatment. These cells can contribute to disease progression and relapse, their elimination being one of the greatest challenges for cure of some children. We have therefore isolated and characterised these cells, to reveal pathways that might be exploited to develop more effective treatments targeting bone marrow disease.
Methods
NB cells were isolated from bone marrow aspirates (BM; n=52) from children with stage 4 disease using immune-magnetic bead selection for the cell surface disialoganglioside GD2. Self-renewal was assessed by plating single cells in low and substrate adherent plates, and in soft agar. Migratory capacity was analysed using a 3D gelatin-based assay. Self-renewing cells were characterised using TaqMan® MicroRNA arrays, reverse transcriptase quantitative polymerase chain reaction (RTqPCR), immunocytology and microscopy.
Results
Infiltration of BM with GD2 positive NB cells was 10% (range 0.02 – 43%). Spheroid forming efficiency from a single cell was 6% (range 0.5-27%) and colony formation efficiency in soft agar 3% (range 0-9%). Migratory cells were identified in all NB cultures; the migration index was highly heterogeneous (126; range 10-428). Cells were isolated that expressed tyrosine hydroxylase and nestin, but not NB84, CD57 or MRP4. Interestingly the ABC transporter protein MRP-1 was expressed in cells from 96% of cultures. Cell cultures could not be established from the GD2 negative cells. Importantly clonal populations of self-renewing cells have been isolated, and propagated. HIF-1, PI3K-AKT and ErbB signalling pathways are highly expressed in self-renewing NB cells (n=38) isolated from the bone marrow, compared to published pathway profiles in primary tumour.
Conclusion
NB cells with heterogeneous self-renewing capacity and a migratory phenotype have been successfully isolated and maintained in culture from BM aspirates taken at diagnosis from children with stage 4 disease. Signalling pathways have been identified which might in the future be exploited for the development of treatment targeting bone marrow disease.