Translational evidence for RRM2 as a prognostic biomarker and therapeutic target in Ewing sarcoma

Abstract

Purpose: Ewing sarcoma (EwS) is a highly aggressive bone- or soft tissue-associated malignancy mostly affecting children, adolescents, and young adults. Although multimodal therapies have strongly improved patients′ overall survival over the past decades, the development of prognostic biomarkers for risk-based patient stratification and more effective therapies with less adverse effects is stagnating. Thus, new personalized medicine approaches are urgently required. Experimental design: Gene expression data of EwS and normal tissues were crossed with survival data to identify highly overexpressed, prognostically relevant, and actionable potential targets. RNA-interference and dose-response assays as well as tissue-microarray analyses were carried out to explore the functional role and druggability of a prominent candidate gene in vitro and in vivo, and to validate its suitability as a prognostic biomarker. Results: Employing a multilayered screening approach, we discover ribonucleotide reductase regulatory subunit M2 (RRM2) as a promising therapeutic target and prognostic biomarker in EwS. Through analysis of two independent EwS patient cohorts, we show that RRM2 mRNA and protein overexpression is associated with an aggressive clinical phenotype and poor patients′ overall survival. In agreement, RRM2 silencing as well as pharmacological inhibition by the specific inhibitor triapine (3-AP) significantly reduces EwS growth in vitro and in vivo. Furthermore, we present evidence that pharmacological RRM2 inhibition by triapine can overcome chemoresistance against doxorubicin or gemcitabine, and synergize with cell cycle checkpoint inhibitors (CHEK1 or WEE1). Conclusions: Based on the aggressive phenotype mediated by and the druggability of RRM2 our results provide a translational rationale for exploiting RRM2 as a novel therapeutic target in EwS and prompt further clinical investigations.

RRM2 enhances MYCN-driven neuroblastoma formation and acts as a synergistic target with CHK1 inhibition

“…The effects of nucleotide inhibition by RNR inhibitors or RRM2 knockdown on CHK1 levels have been reported by several teams ( 61 , 62 ). Particularly instructive is the recent work of Ohmura et al in Ewing sarcoma ( 23 ), who demonstrated that, upon exposure to the gemcitabine RNR inhibitor, total CHK1 is down-regulated together with down-regulation of global protein levels. These authors also showed that, upon RRM2 knockdown, similar results are observed.…”

“…Evidence for a more direct role of RRM2 in cancer formation or maintenance comes from mouse models in which increased RRM2 expression promotes lung ( 19 ), breast ( 20 ), and prostate cancer ( 21 ). Furthermore, RRM2 dependency was demonstrated in BRAF V600E -driven melanoma ( 22 ) and Ewing sarcoma ( 23 ). Of further interest, RRM2 was shown to be the target of synthetic lethal interaction with G2 Checkpoint Kinase (WEE1) inhibition in H3K36me3-deficient cancers ( 12 ).…”