Abstract 6275: Targeting RRM2 by triapine sensitizes glioblastoma to radiotherapy

Abstract

Abstract Glioblastoma multiforme (GBM) remains characterized by poor clinical outcomes and limited treatment options. Currently, the standard of care for patients with this disease is surgery with radiation therapy and concurrent and adjuvant temozolomide. However, most patients succumb to the disease within the first 15 months after diagnosis. Therefore, effective treatment regimens are desperately needed. Exacerbated cell proliferation as well as repair of DNA damage induced by chemoradiation requires a constant supply of dNTPs. Ribonucleotide reductase (RNR) is the key enzyme for the synthesis of dNTPs and is a complex formed by two subunits: RRM1 and RRM2 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3AP - commercially Triapine) is a molecule that potently inhibits RRM2 by affecting its active site, and has been shown to cross the brain-blood barrier (Jiang et al. 2006. PMID: 16834759). We herein report that triapine induces DNA replication stress and sensitizes GBM cells to radiation. Analyses of available datasets including TCGA show that RRM2 is overexpressed in GBM and lower grade glioma (LGG), and a higher expression of RRM2 associates with worse overall survival and disease-free survival of GBM and LGG patients. Nevertheless, RRM2 levels do not change between initial and recurrent tumors (Wang et al. 2017. PMID: 28697342). Using human GBM cell lines LN229, LN18 and U251, we have performed cytotoxicity assays and clonogenic radiation assays. The IC50 of triapine in these cell lines are between 1-2 μM. We find that triapine significantly radiosensitizes LN229, LN18 and U251 cells. Consistent with the role of RRM2 in dNTPs biosynthesis, triapine treatment of GBM cells induces robust phosphorylation of CHK1 at S345, which is accompanied by elevated gamma H2AX. Importantly, we reveal that triapine promotes ionizing radiation induced phosphorylation of CHK2 at T68. Acknowledging the increasing concerns about using established cell lines for GBM studies, we are currently moving to validate our results in primary GBM cell lines. Our results demonstrate that RRM2 is overexpressed in glioblastoma and targeting RRM2 with triapine enhances radiation-induced DNA damage leading to radiosensitization of glioblastoma cells. Our findings suggest that triapine is a promising agent for the sensitization of glioblastoma to radiotherapy. Citation Format: Sergio Corrales-Guerrero, Erica H. Bell, Arnab Chakravarti, Changxian Shen, Terence M. Williams. Targeting RRM2 by triapine sensitizes glioblastoma to radiotherapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6275.