GSE161899
The dependency factor RRM2 at the nexus of a copy number driven regulatory network and a target for synthetic lethal interactions with replication stress checkpoint addiction in high-risk neuroblastoma [siRNA_RRM2]
Neuroblastoma is a pediatric tumor originating from the sympathetic nervous system responsible for 10-15% of all childhood cancer deaths. Half of all neuroblastoma patients present with high-risk disease at diagnosis despite intensive multi-modal therapies of which nearly 50% relapse and die of their disease. In contrast to the overall paucity of mutations, high-risk neuroblastoma nearly invariably present with recurrent somatic segmental chromosome copy number variants. For several focal aberrations (e.g. MYCN and LIN28B amplification), the direct role in tumor formation has been established. However, for recurrent aberrations, such as chromosome 2p and 17q gains, the identification of genes contributing to tumor initiation or progression has been challenging due to the scarcity of small segmental gains or amplifications. In this study, we identified and functionally evaluated the 'ribonucleotide reductase regulatory subunit 2' (RRM2) as a top-ranked 2p putative co-driver and therapeutic target in high-risk neuroblastoma enforcing replicative stress resistance. RRM2 dependency was shown in vitro through knockdown in neuroblastoma cells, with transcriptome analysis revealing downregulation of pediatric tumor markers. Transgenic zebrafish lines expressing RRM2 in immature sympathoblasts were crossed with a d?h-MYCN transgenic zebrafish line, with RRM2 overexpression dramatically increasing tumor penetrance from 20% to nearly 100%, accelerating neuroblastoma formation with tumors formed as early as 5 weeks of age in the double positive fish.  Through CasID, we aimed to identify RRM2 promotor bound proteins. and enriched amongst others HEXIM1 and the NurRD complex. Importantly, adaptive responses regulating RRM2 expression are also controlled by ATR/CHK1 and WEE1 cell cycle checkpoint kinases, as shown by pharmacological inhibition with small molecule inhibitors. We provide in vitro and in vivo data showing that RRM2 inhibition with triapine strongly sensitizes neuroblastoma cells to CHK1 inhibition and that combined treatment could robustly induce upregulated PD-L1 surface expression. Altogether, we propose RRM2 as a bona fide target to explore novel synergistic drug combinations through phase I clinical trials. Overall design: IMR32 and CLBGA neuroblastoma cells were transfected with 100 nM of two independent RRM2 targeting siRNAs (s12361 and s12362, Ambion, Thermo Fischer Scientific) or a control siRNA  (#AM4635, Ambion, Thermo Fischer Scientific) using the Neon transfection Kit (Cat. No. MPK10096). RNA was collected 72h post-transfection. RNA extraction was performed according to  the manufacturer's instructions of miRNeasy kit (Qiagen) including on-column DNase treatment and nanodrop (Thermo Scientific) was used to determine the concentration.