Phospho-proteomic Analysis of Neuroblastoma Tumor Initiating Cell Signaling Pathways: Identification of Src Family and B Cell Receptor Signaling as Novel Drug Targets

Neuroblastoma (NB) is the most common extra-cranial solid tumor in children. Recently discovered neuroblastoma tumor-initiating cells (NB-TICs) have many properties of cancer stem cells and form tumors with as few as 10 cells. To elucidate the signaling pathways driving NB- TIC survival and proliferation, we surveyed the phospho-tyrosine containing subset of the NB- TIC proteome. Over 300 phosphorylated proteins were identified, including 21 tyrosine kinases of which several belong to the Src kinase family. Using bioinformatics tools, several hematopoietic signaling pathways were identified, including the B cell receptor (BCR) pathway. Further proteomic approaches substantiated molecular hematopoietic features in NB-TICs. Inhibitors of BCR proximal kinases SYK and SFKs were cytotoxic to NB-TICs. Clinically utilized inhibitors of SFKs induce apoptosis in NB-TICs. Targeting hematopoietic survival pathways in NB-TICs from the bone marrow, which have thus far not been predicted to play a role in this neural malignancy, may provide new drug therapies for NB.MAS