11q deletion or ALK activity curbs DLG2 expression to maintain an undifferentiated state in neuroblastoma

High-risk neuroblastomas typically display an undifferentiated or poorly differentiated morphology. It is therefore vital to understand molecular mechanisms that block the differentiation process. We identify an important role for oncogenic ALK-ERK1/2-SP1 signaling in the maintenance of undifferentiated neural crest-derived progenitors through the repression of DLG2, a candidate tumor suppressor gene in neuroblastoma. DLG2 is expressed in the murine "bridge signature'' that represents the transcriptional transition state when neural crest cells or Schwann cell precursors differentiate to chromaffin cells of the adrenal gland. We show that the restoration of DLG2 expression spontaneously drives neuroblastoma cell differentiation, high-lighting the importance of DLG2 in this process. These findings are supported by genetic analyses of high-risk 11q deletion neuroblastomas, which identified genetic lesions in the DLG2 gene. Our data also suggest that further exploration of other bridge genes may help elucidate the mechanisms underlying the differentiation of NC-derived progenitors and their contribution to neuroblastomas

Molecular and genetic studies in high-risk neuroblastoma

Neuroblastoma is the most common and deadly cancer in the first year of life. Children with high-risk neuroblastoma have a very poor prognosis, despite heavy multimodal treatment, with less than 50% of 5 years of overall survival. Unfortunately, between 50-60% of high-risk neuroblastoma patients will eventually suffer a relapse with a survival rate of less than 10%. For this reason, a better understanding of the interplay between genetic abnormalities within the nervous system context is necessary to improve patient stratification or aid therapeutic strategies that can ultimately lead to increased patient survival. In order to find molecular profiles that predispose to development of high-risk neuroblastoma or contribute to the relapse, metastatic or non-responsive status of the tumor, we performed comprehensive molecular characterization of neuroblastoma tumors and cell lines by SNP-microarrays and next generation sequencing techniques in combination with functional exploration of novel recurrent somatic aberrations. Through our large-scale studies, we confirmed the genetic stability of neuroblastoma PDOXs over serial passaging, explored intra-tumoral heterogeneity of neuroblastoma and monitored a set of primary/relapsed neuroblastoma tumors, highlighting the recurrence of alterations of MAPK signaling, cell cycle progression and telomere activity pathways. Furthermore, we detected and investigated a recurrent structural alteration in LSAMP which appears to be a tumor suppressor gene in neuroblastoma. We also characterized a highly aggressive subgroup of neuroblastoma tumors, which presented a high-grade amplification of two loci at 12q, and our in vitro results indicated possible tumor inhibition routes through CDK4 and MDM2 inhibition. To conclude, genome-wide analyses with powerful techniques, such as next generation sequencing, are useful not only for research purposes but also as a clinical tool

Whole-genome sequencing of recurrent neuroblastoma reveals somatic mutations that affect key players in cancer progression and telomere maintenance

Neuroblastoma is the most common and deadly childhood tumor. Relapsed or refractory neuroblastoma has a very poor prognosis despite recent treatment advances. To investigate genomic alterations associated with relapse and therapy resistance, whole-genome sequencing was performed on diagnostic and relapsed lesions together with constitutional DNA from seven children. Sequencing of relapsed tumors indicates somatic alterations in diverse genes, including those involved in RAS-MAPK signaling, promoting cell cycle progression or function in telomere maintenance and immortalization. Among recurrent alterations, CCND1-gain, TERT-rearrangements, and point mutations in POLR2A, CDK5RAP, and MUC16 were shown in >= 2 individuals. Our cohort contained examples of converging genomic alterations in primary-relapse tumor pairs, indicating dependencies related to specific genetic lesions. We also detected rare genetic germline variants in DNA repair genes (e.g., BARD1, BRCA2, CHEK2, and WRN) that might cooperate with somatically acquired variants in these patients with highly aggressive recurrent neuroblastoma. Our data indicate the importance of monitoring recurrent neuroblastoma through sequential genomic characterization and that new therapeutic approaches combining the targeting of MAPK signaling, cell cycle progression, and telomere activity are required for this challenging patient group

Patient-derived xenograft models reveal intratumor heterogeneity and temporal stability in neuroblastoma

Patient-derived xenografts (PDX) and the Avatar, a single PDX mirroring an individual patient, are emerging tools in preclinical cancer research. However, the consequences of intratumor heterogeneity for PDX modeling of biomarkers, target identification, and treatment decisions remain underexplored. In this study, we undertook serial passaging and comprehensive molecular analysis of neuroblastoma orthotopic PDXs, which revealed strong intrinsic genetic, transcriptional, and phenotypic stability for more than 2 years. The PDXs showed preserved neuroblastoma-associated gene signatures that correlated with poor clinical outcome in a large cohort of patients with neuroblastoma. Furthermore, we captured spatial intratumor heterogeneity using ten PDXs from a single high-risk patient tumor. We observed diverse growth rates, transcriptional, proteomic, and phosphoproteomic profiles. PDX-derived transcriptional profiles were associated with diverse clinical characteristics in patients with high-risk neuroblastoma. These data suggest that high-risk neuroblastoma contains elements of both temporal stability and spatial intratumor heterogeneity, the latter of which complicates clinical translation of personalized PDX-Avatar studies into preclinical cancer research

Amplification of CDK4 and MDM2 : a detailed study of a high-risk neuroblastoma subgroup

In neuroblastoma, MYCN amplification and 11q-deletion are important, although incomplete, markers of high-risk disease. It is therefore relevant to characterize additional alterations that can function as prognostic and/or predictive markers. Using SNP-microarrays, a group of neuroblastoma patients showing amplification of one or multiple 12q loci was identified. Two loci containing CDK4 and MDM2 were commonly co-amplified, although amplification of either locus in the absence of the other was observed. Pharmacological inhibition of CDK4/6 with ribociclib or abemaciclib decreased proliferation in a broad set of neuroblastoma cell lines, including CDK4/MDM2-amplified, whereas MDM2 inhibition by Nutlin-3a was only effective in p53(wild-type) cells. Combined CDK4/MDM2 targeting had an additive effect in p53(wild-type) cell lines, while no or negative additive effect was observed in p53(mutated) cells. Most 12q-amplified primary tumors were of abdominal origin, including those of intrarenal origin initially suspected of being Wilms' tumor. An atypical metastatic pattern was also observed with low degree of bone marrow involvement, favoring other sites such as the lungs. Here we present detailed biological data of an aggressive neuroblastoma subgroup hallmarked by 12q amplification and atypical clinical presentation for which our in vitro studies indicate that CDK4 and/or MDM2 inhibition also could be beneficial