biomedicines Article Clinicopathological and Functional Evaluation Reveal NBS1 as a Predictor of Platinum Resistance in Epithelial Ovarian Cancers Adel Alblihy 1,2 , Muslim L. Alabdullah 1,3 , Reem Ali 1 , Mashael Algethami 1 , Michael S. Toss 3 , Nigel P. Mongan 4,5 , Emad A. Rakha 3 and Srinivasan Madhusudan 1,6, *   Citation: Alblihy, A.; Alabdullah, M.L.; Ali, R.; Algethami, M.; Toss, M.S.; Mongan, N.P.; Rakha, E.A.; Madhusudan, S. Clinicopathological and Functional Evaluation Reveal NBS1 as a Predictor of Platinum Resistance in Epithelial Ovarian Cancers. Biomedicines 2021, 9, 56. https://doi.org/10.3390/ biomedicines9010056 Received: 7 December 2020 Accepted: 29 December 2020 Published: 8 January 2021 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional clai- ms in published maps and institutio- nal affiliations. Copyright: © 2021 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Translational Oncology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham Biodiscovery Institute, Nottingham NG5 1PB, UK; msxamal@exmail.nottingham.ac.uk (A.A.); msxmla@exmail.nottingham.ac.uk (M.L.A.); drreemali7@gmail.com (R.A.); msxma58@exmail.nottingham.ac.uk (M.A.) 2 Medical Center, King Fahad Security College (KFSC), Riyadh 11461, Saudi Arabia 3 Academic Pathology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham Biodiscovery Institute, Nottingham NG5 1PB, UK; mszmst@exmail.nottingham.ac.uk (M.S.T.); mrzear1@exmail.nottingham.ac.uk (E.A.R.) 4 School Veterinary Medicine and Science, Faculty of Medicine and Health Sciences, University of Nottingham Biodiscovery Institute, Nottingham NG7 2RD, UK; svznpm@exmail.nottingham.ac.uk 5 Department of Pharmacology, Weill Cornell Medicine, New York, NY 10065, USA 6 Department of Oncology, Nottingham University Hospitals, Nottingham NG5 1PB, UK * Correspondence: srinivasan.madhusudan@nottingham.ac.uk Abstract: Platinum resistance seriously impacts on the survival outcomes of patients with ovarian cancers. Platinum-induced DNA damage is processed through DNA repair. NBS1 is a key DNA repair protein. Here, we evaluated the role of NBS1 in ovarian cancers. NBS1 expression was investigated in clinical cohorts (protein level (n = 331) and at the transcriptomic level (n = 1259)). Pre-clinically, sub-cellular localization of NBS1 at baseline and following cisplatin therapy was tested in platinum resistant (A2780cis, PEO4) and sensitive (A2780, PEO1) ovarian cancer cells. NBS1 was depleted and cisplatin sensitivity was investigated in A2780cis and PEO4 cells. Nuclear NBS1 overexpression was associated with platinum resistance (p = 0.0001). In univariate and multivariate analysis, nuclear NBS1 overexpression was associated with progression free survival (PFS) (p-values = 0.003 and 0.017, respectively) and overall survival (OS) (p-values = 0.035 and 0.009, respectively). NBS1 mRNA overexpression was linked with poor PFS (p = 0.011). Pre-clinically, following cisplatin treatment, we observed nuclear localization of NBS1 in A2780cis and PEO4 compared to A2780 and PEO1 cells. NBS1 depletion increased cisplatin cytotoxicity, which was associated with accumulation of double strand breaks (DSBs), S-phase cell cycle arrest, and increased apoptosis. NBS1 is a predictor of platinum sensitivity and could aid stratification of ovarian cancer therapy. Keywords: NBS1; ovarian cancer; platinum sensitization; biomarker 1. Introduction Overall survival outcomes for patients with advanced ovarian cancer remains poor despite platinum-based chemotherapy [1–4]. The development of platinum resistance and disease recurrence is a formidable clinical problem [5–7]. Although the mechanism of action of platinating agents (carboplatin, cisplatin) is complex, the cytotoxicity predomi- nantly is related to their ability to induce intra-strand or inter-strand DNA cross-links in cancer cells [8]. If unrepaired, the DNA cross-links can get converted to double strand breaks (DSBs) during replication. Accumulation of DSBs can promote cancer cell death [8]. However, enhanced DNA repair capacity and processing of DSBs can lead to platinum re- sistance in cancer [9]. Recently, in platinum sensitive sporadic or BRCA germ-line deficient Biomedicines 2021, 9, 56. https://doi.org/10.3390/biomedicines9010056 https://www.mdpi.com/journal/biomedicines