ESTRO 2020 Abstract Book

S103 ESTRO 2020

(TMZ) treatment in vitro , and showed statistically significant smaller tumor size (p<0.01) and prolonged survival (p=0.001) in vivo . In addition, miR-146a is downregulated in glioma cancer stem cells, and overexpression of miR-146a significantly inhibited glioma cancer stem cell self-renewal using sphere formation assay. We also found that overexpression of miR-146a significantly inhibited NF-κB and ERK activities. Conclusion Our data suggest, for the first time, that miR-146a predicts favorable prognosis for GBM patients and sensitizes primary GBM cells to TMZ treatment in vitro and in vivo through regulating glioma stem cells. Importantly, miR- 146a may prove to be a master switch shutting off NF-κB, ERK, as well as other pathways and may overcome redundancies among these pathways leading to resistance. Funding: R01CA108633, R01CA169368, U10CA180850- 01(NCI), Brain Tumor Funders Collaborative Grant, and The Ohio State University CCC (all to AC), Bohnenn Fund (to PR). OC-0207 Avoidance of DNA replication stress leads to radioresistance in stem cell-like TNBC F. Meyer 1 , A. Engel 1 , B. Riepen 1 , U. Schumacher 2 , A. Dubrovska 3 , C. Petersen 4 , C. Peitzsch 3 , L. Hein 3 , S. Werner 5 , H. Wikmann 5 , K. Rothkamm 1 , K. Borgmann 1 1 University Medical Center Hamburg - Eppendorf UKE, Radiation Biology/Experimental Radiooncology, Hamburg, Germany ; 2 University Medical Center Hamburg - Eppendorf UKE, Institute for Anatomy and Experimental Anatomy, Hamburg, Germany ; 3 Technical University Dresden, OncoRay, Dresden, Germany ; 4 University Medical Center Hamburg - Eppendorf UKE, Clinic for Radiotherapy, Hamburg, Germany ; 5 University Medical Center Hamburg - Eppendorf UKE, Tumorbiology, Hamburg, Germany Purpose or Objective Despite postoperative radiotherapy, triple-negative breast cancer (TNBC) often develops local recurrences and distant metastases. This is attributed to an increased proportion of radiation-resistant tumor stem cells (CSC). CSC are characterized by a more effective DNA damage response and repair processes as well as reduced oxidative stress. However, it is still unclear how DNA repair pathways and the avoidance of oxidative stress determine the radiation resistance of CSC. This project aims to figure out resistance mechanisms of CSC and strategies to overcome their intrinsic therapy resistance Material and Methods The investigations were performed in three isogenic MDA- MB-231 TNBC cell lines, their respective radiation resistant subclones selected by repeated irradiation (10x4Gy). Luminal MCF7 cells served as controls. Expression of Homologous recombination (HR) -related and stem-cell factors was determined and DNA repair in general (53BP1) as well as Replication stress (RPA/yH2AX foci) and HR functionality (RAD51 foci, plasmid reporter assay) were analyzed. Replication processes were examined using the DNA fiber assay, Mitotracker-assays were also performed. The radiosensitizing effect of DNA-repair and S-phase specific inhibitors was analyzed by colony assay and correlated with expression profiles of stem cell markers and DNA repair proteins in the METABRIC database Results An increased expression of the stem cell markers ZEB1 and ALDH1 and a significantly increased activity of ALDH1 was observed in all radioresistant clones. After irradiation, survival in the clonal subpopulation was significantly increased and the number of cellular mitochondria decreased compared to the original cell line. In accordance to this, the radioresistant subclones showed a significantly lower number of 53BP1 foci after irradiation in S-Phase (p= 0.0001), indicating an improved DNA repair by HR and a lower amount of reactive oxygen species

immunohistochemical staining of CAIX expression was analyzed. Results DTPA-B9 was radiolabeled with 111 In at a specific activity of 4 MBq/µg. [ 111 In]In-DTPA-B9 bound to SKRC-52 cells with high affinity (IC 50 = 11.3 nm, Kd = 27.2 nM) and the internalization rate of the tracer was relatively low (K e = 0.01). A protein dose of 5 µg resulted in the highest uptake in SCCNij153 tumors in vivo (1.05±0.14%ID/g), with tumor- to-blood and tumor-to-muscle ratios of 11.5 and 24.7, respectively. Unlabeled B9 reduced tumor uptake to 0.30±0.03%ID/g and irrelevant [ 111 In]In-DTPA-R2 showed tumor uptake of 0.20±0.14%ID/g. Gelofusin did not significantly alter kidney uptake of [ 111 In]In-DTPA-B9. Immunohistochemistry and autoradiography images showed co-localization of [ 111 In]In-DTPA-B9 and expression of CAIX. Conclusion [ 111 In]In-DTPA-B9 VHH shows specific targeting of CAIX expression in head-and-neck cancer xenografts. In follow- up studies we will compare this tracer to other CAIX imaging tracers and we will determine its potential for treatment selection and monitoring of hypoxia responses to therapy. OC-0205 NOTCH inhibition promotes stem cell renewal and epithelial integrity in irradiated bronchial cells OC-0206 Epigenetic silencing of miR-146a drives tumor progression and therapeutic resistance in glioblastoma T. Cui 1 , E.H. Bell 1 , J. McElroy 2 , B. Johnson 1 , E. Sebastian 1 , K. Liu 3 , P.M. Gulati 1 , A.P. Becker 1 , M. Geurts 4 , A. Gray 3 , J. Fleming 1 , S. Beyer 1 , M. Venere 1 , J. Haque 1 , Q. Wang 1 , P. Robe 5 , A. Chakravarti 1 1 Arthur G. James Hospital/Ohio State Comprehensive Cancer Center, Department of Radiation Oncology, Columbus, USA ; 2 The Ohio State University Center for Biostatistics, Department of Biomedical Informatics, Columbus, USA ; 3 The Ohio State University College of Medicine, Department of Radiation Oncology, Columbus, USA ; 4 Erasmus MC Cancer Center, Department of Neurology, Utrecht, The Netherlands ; 5 Brain Center Rudolf Magnus- University Medical Center Utrecht, Department of Neurology and Neurosurgery, Utrecht, The Netherlands Purpose or Objective Glioblastomas (GBMs) are the most aggressive primary brain tumors, with an average survival of less than 15 months despite decades of translational investigation. microRNAs (miRNAs) function as post-transcriptional regulators, and are promising novel biomarkers in GBM. The aims of this study are: 1) to investigate novel miRNAs biomarkers that affect tumorigenesis and therapeutic sensitivity, and 2) to study the underlying molecular Total RNAs were isolated from 268 FFPE tumor samples, Nanostring v3 was performed for miRNA expression analysis followed by univariable (UVA) and multivariable (MVA) survival analyses. Cell proliferation, invasion, and apoptosis assays were conducted to define the role of miR- 146a in GBM tumorigenesis and therapeutic response. Results UVA analyses demonstrated that miR-146a is one of the top miRNAs that correlated with better prognosis in GBM patients (p=9.21E-05), which was independent of MGMT promoter methylation by MVA analyses (p<0.001). miR- 146a expression was significantly downregulated in recurrent GBM tumors compared with the paired primary GBM tumors (p=0.003). Overexpression of miR-146a significantly inhibited tumor cell growth and sensitized patient-derived primary GBM cells to temozolomide mechanisms in GBM. Material and Methods Withdrawn from presentation