Role of stemness-related molecules in neuroblastoma.

Neuroblastoma (NB) is the most common pediatric solid malignant tumor derived from the sympathetic nervous system. High-risk NB is still one of the most difficult tumors to cure, with only 40% long-term survival despite intensive multimodal therapy. The clinical presentation and treatment response of advanced NB, which results in relapse and a refractory state after a good response to the initial chemotherapy, suggests that cancer stem cells (CSCs) likely exist in NB tumors. Putative CSCs using primary tumor sphere formation from NB patients were reported previously, and several molecules will be elucidated from the tumor sphere to develop CSC-targeting therapies. Recently, our group reported that a CSC marker for several malignancies, CD133, and the stemness-related polycomb BMI1 have functions to repress NB cell differentiation. Depletion of CD133 or BMI1 effectively induced neurite elongation and marker molecules for differentiation in NB cells. Of note, CD133-related NB cell differentiation and RET (rearranged during transfection) repression were considerably dependent on p38MAPK and phosphoinositide 3-kinase (PI3K)/AKT pathways. Intriguingly, both CD133 and BMI1 also have a role in xenograft tumor formation and tumor sphere formation. These observations suggest that CD133 and BMI1 may be candidates for the development of CSC-targeting therapies for refractory NB patients.