Background Regorafenib is an inhibitor of multiple kinases with aberrant expression and activity in neuroblastoma tumours that have potential roles in neuroblastoma pathogenesis. Methods We evaluated neuroblastoma cells treated with regorafenib for cell viability and confluence, and analysed treated cells for apoptosis and cell cycle progression. We evaluated the efficacy of regorafenib in vivo using an orthotopic xenograft model. We evaluated regorafenib-mediated inhibition of kinase targets and performed reverse-phase protein array (RPPA) analysis of neuroblastoma cells treated with regorafenib. Lastly, we evaluated the efficacy and effects of the combination of regorafenib and 13-cis-retinoic acid on intracellular signalling. Results Regorafenib treatment resulted in reduced neuroblastoma cell viability and confluence, with both induction of apoptosis and of cell cycle arrest. Regorafenib treatment inhibits known receptor tyrosine kinase targets RET and PDGFRβ and intracellular signalling through the RAS/MAPK, PI3K/Akt/mTOR and Fos/Jun pathways. Regorafenib is effective against neuroblastoma tumours in vivo, and the combination of regorafenib and 13-cis-retinoic acid demonstrates enhanced efficacy compared with regorafenib alone. Conclusions The effects of regorafenib on multiple intracellular signalling pathways and the potential additional efficacy when combined with 13-cis-retinoic acid represent opportunities to develop treatment regimens incorporating regorafenib for children with neuroblastoma.

Background Identifying mechanisms of medulloblastoma recurrence is a key to improving patient survival, and targeting treatment-resistant subpopulations within tumors could reduce disease recurrence. Expression of the granulocyte colony-stimulating factor receptor (G-CSF-R, CD114) is a potential marker of cancer stem cells, and therefore we hypothesized that a subpopulation of medulloblastoma cells would also express CD114 and would demonstrate chemoresistance and responsiveness to G-CSF. Methods Prevalence of CD114-positive (CD114+) cells in medulloblastoma cell lines, patient-derived xenograft (PDX) tumors, and primary patient tumor samples were assessed by flow cytometry. Growth rates, chemoresistance, and responses to G-CSF of CD114+ and CD114-negative (CD114−) cells were characterized in vitro using continuous live cell imaging and flow cytometry. Gene expression profiles were compared between CD114+ and CD114− medulloblastoma cells using quantitative RT-PCR. Results CD114+ cells were identifiable in medulloblastoma cell lines, PDX tumors, and primary patient tumors and have slower growth rates than CD114− or mixed populations. G-CSF accelerates the growth of CD114+ cells, and CD114+ cells are more chemoresistant. The CD114+ population is enriched when G-CSF treatment follows chemotherapy. The CD114+ population also has higher expression of the CSF3R, NRP-1, TWIST1, and MYCN genes. Conclusions Our data demonstrate that a subpopulation of CD114+ medulloblastoma cells exists in cell lines and tumors, which may evade traditional chemotherapy and respond to exogenous G-CSF. These properties invite further investigation into the role of G-CSF in medulloblastoma therapy and methods to specifically target these cells.

No abstract

Background Neuroblastoma is a pediatric malignancy with a high frequency of metastatic disease at initial diagnosis. Neuroblastoma tumors have few recurrent protein-coding mutations but contain extensive somatic copy number alterations (SCNAs) suggesting that mutations that alter gene dosage are important drivers of tumorigenesis. Here, we analyze allele-specific expression in 96 high-risk neuroblastoma tumors to discover genes impacted by cis-acting mutations that alter dosage. Results We identify 1043 genes with recurrent, neuroblastoma-specific allele-specific expression. While most of these genes lie within common SCNA regions, many of them exhibit allele-specific expression in copy neutral samples and these samples are enriched for mutations that are predicted to cause nonsense-mediated decay. Thus, both SCNA and non-SCNA mutations frequently alter gene expression in neuroblastoma. We focus on genes with neuroblastoma-specific allele-specific expression in the absence of SCNAs and find 26 such genes that have reduced expression in stage 4 disease. At least two of these genes have evidence for tumor suppressor activity including the transcription factor TFAP2B and the protein tyrosine phosphatase PTPRH. Conclusions In summary, our allele-specific expression analysis discovers genes that are recurrently dysregulated by both large SCNAs and other cis-acting mutations in high-risk neuroblastoma.

Expression of the UBE4B ubiquitin ligase is strongly associated with neuroblastoma patient outcomes, but the functional roles of UBE4B in neuroblastoma pathogenesis are not known. We evaluated interactions of UBE4B with the E3 ubiquitin ligase ITCH/AIP4 and the effects of UBE4B expression on Ku70 and c-FLIPL ubiquitination and proteasomal degradation by co-immunoprecipitation and Western blots. We also evaluated the role of UBE4B in apoptosis induced by histone deacetylase (HDAC) inhibition using Western blots. UBE4B binding to ITCH was mediated by WW domains in the ITCH protein. ITCH activation led to ITCH-UBE4B complex formation and recruitment of Ku70 and c-FLIPL via ITCH WW domains, followed by Ku70 and c-FLIPL Lys48/Lys63 branched polyubiquitination and proteasomal degradation. HDAC inhibition induced Ku70 acetylation, leading to release of c-FLIPL and Bax from Ku70, increased Ku70 and c-FLIPL Lys48/Lys63 branched polyubiquitination via the ITCH-UBE4B complex, and induction of apoptosis. UBE4B depletion led to reduced polyubiquitination and increased levels of Ku70 and c-FLIPL and to reduced apoptosis induced by HDAC inhibition via stabilization of c-FLIPL and Ku70 and inhibition of caspase 8 activation. Our results have identified novel interactions and novel targets for UBE4B ubiquitin ligase activity and a direct role of the ITCH-UBE4B complex in responses of neuroblastoma cells to HDAC inhibition, suggesting that the ITCH-UBE4B complex plays a critical role in responses of neuroblastoma to therapy and suggesting a potential mechanism underlying the association of UBE4B expression with neuroblastoma patient outcomes.