ESTRO 2020 Abstract book

S268 ESTRO 2020

SKMEL28 and G361, p<0.0001 for RO4929097 effect, and p=0.62, p=0.49, p=0.51 for radiation effect respectively) (Figure 1, C & D) , confirming our earlier observations of impairment of cell migration with this approach.

gliomas on the basis of their IDH 1/2 mutation status such that the IDH1/2 wild type tumors are more aggressive compared to IDH1/2 mutant tumors. In spite of such distribution, both groups are treated similarly by the Stupp protocol. Therefore, there is a need of biomarkers and therapeutic targets to improve the treatment and also provide better patient stratification. In this study, we identified TRIB1, a Ser/Thr pseudokinase that acts as a scaffold protein to cause Ubiquitin Proteasome System mediated degradation of target proteins in the cell. TRIB1 has also been associated with survival of prostate cancer cells and poor disease prognosis. Material and Methods We utilized a patient-centered reverse translational approach to identify novel therapeutic targets. TRIB1 was identified by statistical association (Cox regression analysis) and logic-based network analyses of the patient- derived data. TRIB1 was functionally validated in vitro by overexpression and knockdown studies. For knockdown of TRIB1, doxycycline inducible system was used. Stable cell lines were created by puromycin selection and cell sorting. Protein levels were detected by western blotting. Results The global methylation analysis on Utrecht GBM cohort revealed that levels of Trib1 promoter methylation is associated with better OS of GBM patients. The TRIB1 promoter was also shown to be less methylated in MGMT unmethylated tumors. We also observed that TRIB1 was induced after radiation exposure. The overexpression of TRIB1 caused a decrease in apoptosis of PDX cell lines after radiation exposure and TMZ treatment. The overexpression of TRIB1 also increased ERK and Akt signaling in PDX cell lines. It was also observed that TRIB1 levels were upregulated in p53-mutant cell lines. Importantly, TRIB1 knockdown resulted in reduced proliferation of PDX cell lines. Conclusion TRIB1 is a promising therapeutic target for glioma therapy because targeting TRIB1 would promote radio-sensitivity of p53 mutant glioma cells and provide an alternative treatment strategy for MGMT unmethylated patients that do not respond to TMZ. Grant support: National Cancer Institute [R01CA169368 (to A.C.), R01CA11522358 (to A.C.), R01CA1145128 (to A.C.), R01CA108633 (to A.C.), R01CA188228 (to A.C., R.B., K.L., and J.B.), 1RC2CA148190 (to A.C.), and U10CA180850–01 (to A.C.)]; A Brain Tumor Funders Collaborative Grant (to A.C.); Ohio State University Comprehensive Cancer Center Award (to A.C.). OC-0451 Radiation response of breast carcinoma cells with enhanced metastatic capacities B. Aschenbrenner 1 , G. Negro 1 , D. Savic 1 , S.K.B. Kranjc Brezar 2 , M. Cemazar 2 , A.C. Coer 3 , G.G. Gašljević 2 , M.S. Sorokin 4 , A. Buzdin 4 , M.C. Callari 5 , U. .G. Ganswindt 6 , S. Skvortsov 1 , I. Skvortsova 7 1 Medical University of Innsbruck-Tyrolean Cancer Research Institute, EXTRO-Lab- Department of Therapeutic Radiology and Oncology, Innsbruck, Austria ; 2 Institute of Oncology Ljubljana- Ljubljana- Slovenia, Experimental Oncology, Ljubljana, Slovenia ; 3 University of Primorska, Faculty of Health Sciences, Izola, Slovenia ; 4 I.M. Sechenov First Moscow State Medical University, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russian Federation ; 5 University of Cambridge, Cancer Research UK Cambridge Institute, Cambridge, United Kingdom ; 6 Medical University of Innsbruck, Department of Therapeutic Radiology and Oncology, Innsbruck, Austria ; 7 Medical University of

There were statistically significant reductions in melanospheres size (Two-way ANOVA, for A375 p<0.0001 for both effects and for SKMEL28 p=0.77 for radiation effect and p<0.0001 for RO4929097 effect) while Notch signalling inhibition, at higher doses reduced the levels of radiation induced gammaH2AX foci signal intensity (Two- way ANOVA, A375 p=0.02, SKMEL28 p=0.005) (Figure 2) .

Conclusion Together with our previous results, combining radiation with Notch signalling inhibition improves efficacy of radiation in melanoma by impairing phenotypic plasticity and by attenuating DNA damage response. We further demonstrate this strategy has the potential to reduce metastatic spread in melanoma by impairing cellular migration. Validation of our results using in-vivo models is warranted. OC-0450 TRIBBLES1 (TRIB1) pseudokinase: a potential therapeutic target in GBM K. Singh 1 , J. Fleming 1 , C. Han 1 , T. Cui 1 , B. Johnson 1 , J. Haque 1 , E.H. Bell 1 , P. Robe 2 , A. Chakravarti 1 1 Ohio State University Comprehensive Cancer Center, Radiation Oncology, Columbus, USA ; 2 UMC Utrecht, Neurosurgery, Utrecht, Netherlands Antilles Purpose or Objective GBM (WHO grade IV) is the most aggressive glioma with a 5-year survival rate of 5%. The current therapeutic regimen involves radiation therapy and concurrent and adjuvant TMZ (Stupp protocol). In 2016 WHO classified