We present a study on neuroblastoma cells, treated with up to six cycles of cyclopamine, an SMO inhibitor of the sonic hedgehog
pathway. Several genes involved in apoptosis, cancer stem cell phenotype, and sonic hedgehog pathway regulation were tested for expression before and after treatments. Also, cell proliferation and colony formation in 2D and 3D assay systems were used. The genes
related to cancer stem cell phenotypes (CD133 and CD15) seemed to increase their expression after exposition to several treatment
cycles, coincident with the idea of neuroblastoma resistance to cyclopamine. MYCN, SMO and BCL-2 equally showed higher expression levels after several cycles of treatment. Cyclopamine treatment of neuroblastoma cells reduced cell proliferation and in vitro
tumorigenesis determined by 3D colony formation assays in soft agar. The treatments also induced apoptosis and increased MYCN
expression. As a whole, we may consider cyclopamine a good inhibitor against neuroblastoma along the first stages of the treatment, while
resistance to this compound can occur later on. More studies on cyclopamine resistance are needed to better approach to neuroblastoma treatment.