High-risk neuroblastoma, a pediatric tumor originating from the sympathetic nervous system, has a low mutation load but highly recurrent somatic DNA copy number variants. Previously, segmental gains and/or amplifications allowed identification of drivers for neuroblastoma development. Using this approach, combined with gene dosage impact on expression and survival, we identified ribonucleotide reductase subunit M2 (RRM2) as a candidate dependency factor further supported by growth inhibition upon in vitro knockdown and accelerated tumor formation in a neuroblastoma zebrafish model coexpressing human RRM2 with MYCN. Forced RRM2 induction alleviates excessive replicative stress induced by CHK1 inhibition, while high RRM2 expression in human neuroblastomas correlates with high CHK1 activity. MYCN-driven zebrafish tumors with RRM2 co-overexpression exhibit differentially expressed DNA repair genes in keeping with enhanced ATR-CHK1 signaling activity. In vitro, RRM2 inhibition enhances intrinsic replication stress checkpoint addiction. Last, combinatorial RRM2-CHK1 inhibition acts synergistic in high-risk neuroblastoma cell lines and patient-derived xenograft models, illustrating the therapeutic potential.

The pediatric extra-cranial tumor neuroblastoma displays a low mutational burden while recurrent copy number alterations are present in most high-risk cases. Here, we identify SOX11 as a dependency transcription factor in adrenergic neuroblastoma based on recurrent chromosome 2p focal gains and amplifications, specific expression in the normal sympatho-adrenal lineage and adrenergic neuroblastoma, regulation by multiple adrenergic specific (super-)enhancers and strong dependency on high SOX11 expression in adrenergic neuroblastomas. SOX11 regulated direct targets include genes implicated in epigenetic control, cytoskeleton and neurodevelopment. Most notably, SOX11 controls chromatin regulatory complexes, including 10 SWI/SNF core components among which SMARCC1, SMARCA4/BRG1 and ARID1A. Additionally, the histone deacetylase HDAC2, PRC1 complex component CBX2, chromatin-modifying enzyme KDM1A/LSD1 and pioneer factor c-MYB are regulated by SOX11. Finally, SOX11 is identified as a core transcription factor of the core regulatory circuitry (CRC) in adrenergic high-risk neuroblastoma with a potential role as epigenetic master regulator upstream of the CRC.

Dear Editor, Soft-tissue sarcomas (STS) are rare, heterogeneous cancers comprising 1% of adult and 15% of paediatric malignancies. Despite optimal treatment, 50%−80% of patients metastasize, even when they attain a status of minimal residual disease (MRD). MRD is achieved through multimodal treatment involving primary tumour resection with wide negative margins. In metastatic setting, systemic therapies are palliative and response rates are low (15%-20%). 1,2 As a result of these poor outcome data, there is a strong need for translationally relevant patient-derived models.Patient-derived xenografts (PDX) are used to investigate novel therapies and guide personalized treatment response. 3 Yet, many PDX models do not reflect the clinical behaviour of human tumours. 4 For STS, commonly used PDX still fail to predict the clinical efficacy of (novel) drugs and indeed, MRD status and subsequent metastatic progression have been poorly modelled in STS-PDX 5 (Table S1). Moreover, currently available STS-PDX models have not been comparatively assessed. In this study we aimed to address this translational gap by creating PDX that mimic MRD status (MRD-PDX), followed by metastatic relapse and examine the most appropriate model. We first engrafted tumour tissue derived from five high-grade STS patients (Table S2) and resected the subsequent primary tumour at a size of 250-450 mm 3 using limb amputation to obtain negative surgical margins, 6 similar to the patient's treatment (Figure 1A). The impact of the site of transplantation (orthotopic [O-PDX] vs subcutaneous [SC-PDX]) and immunodeficiency status of the host animal (NOD scid gamma [NSG] vs Swiss nu/nu mice) on primary tumour growth, MRD and disease progression (local recurrence and metastasis) were directly compared for four patients (Figure 1B). PDX were followed up to 1 year after tumour resection. MRI monitored primary tumour growth, MRD and metastatic relapse (Figure 1A). Histopathology and copy number variation (CNV) sequencing evaluated tumour characteristics.