Molecular aspects of high-risk neuroblastoma and novel therapeutic opportunities

Abstract

Neuroblastoma is a highly heterogenous cancer of childhood. High-risk disease has a poor prognosis with survival around 50% and cured patients suffer treatment related late effects. Better therapy is needed. Increased knowledge of the molecular biology of high-risk neuroblastomas is essential to devise new treatments. High-risk neuroblastomas are frequently MYCN-amplified (MNA). MNA is correlated to enlarged nucleoli due to increased ribosome biogenesis. The MYCN-product, MycN, has been shown to upregulate genes involved in ribosome biogenesis in neuroblastoma cells. Deregulated microRNA (miRNA)-expression patterns have emerged as a feature of MNA and high-risk neuroblastoma. Also, in recent years, exosomes have been shown to provide a way for secretion of miRNAs, but the exosomal miRNA-content in neuroblastoma has not been characterized. We aimed to identify novel aspects of the molecular biology underpinning high-risk neuroblastomas with an emphasis on MYCN, ribosomal-RNA and miRNAs. In paper 1 we mined publically available RNA-expression datasets from neuroblastoma patients and found that high-risk and MNA-neuroblastomas overexpressed genes involved in ribosome biogenesis. This led us to investigate the effects of small molecular inhibitors of RNA polymerase I (quarfloxin and CX-5461) in neuroblastoma cell lines; we found that this class of molecules effectively reduced the growth of MNA-neuroblastoma cells and xenografts. In paper 2 we characterized the tumor suppressor miR-193b in neuroblastoma and showed this miRNA was expressed at low levels in tumors. Overexpression of miR-193b in cell lines induced growth arrest and cell death through targeting of CCND1, MCL1 and MYCN. In paper 3 we characterized the miRNA-content of exosomes derived from two different MNA-cell lines and discovered that exosomes contained a distinct profile of miRNAs predicted to regulate pathways important in cancer. In conclusion, the discoveries presented in this thesis, can lead to future novel therapies and biomarkers in high-risk neuroblastoma.