ESTRO 37 Abstract book

ESTRO 37

S594

pathway activation, and IR-induced treatment resistance. Inducible, shRNA-mediated silencing of ADAM17 or targeting of ADAM17 with the small molecular inhibitor TMI-005 suppressed IR-induced shedding of these factors, downregulated receptor tyrosine kinase signaling in target cells and enhanced IR-induced cytotoxicity in vitro and in vivo in tumors derived from otherwise cetuximab- resistant cells. Likewise, also treatment with a novel, clinically relevant ADAM17-directed monoclonal antibody, which was previously shown to inhibit growth of tumor cell lines derived from multiple tumor entities, led to a tumor growth delay in A549-derived tumor xenografts in combination with IR. In addition, targeting of ADAM17 interfered with the chromatin structure, decreased the basal level of SUV39H1 and abolished a short-term increase of the SUV39H1 protein in response to irradiation. Surprisingly decreased amounts of residual yH2AX were detected in ADAM17-depleted cells after irradiation despite their increased radiosensitivity in comparison to wildtype cells. At the same time, DNA damage signaling via ATR/Chk1 was impaired in ADAM17- deficient cells, implying an ADAM17-mediated deregulation of the DNA damage response and pointing towards a novel mechanism of radiosensitization by ADAM17 targeting. Conclusion Our findings demonstrate a mechanistic link between IR- induced ADAM17 activity and treatment resistance in NSCLC cells. Our data point towards a novel link between ADAM17, regulation of the chromatin state and the DNA damage response. We demonstrate that the impact of targeting ADAM17 is more pleiotropic than just diminishing ErbB signaling and provide a sound rationale for positioning ADAM17 inhibitors as radiosensitizers to improve treatment of NSCLC. PO-1057 MiR-1246 increases the radiation resistance of non-small cell lung cancer by activation of autophagy L. Fan 1 1 Shandong Cancer Hospital, Radiology, Jinan, China Purpose or Objective Radiation is a major treatment for patients with non- small cell lung cancer, especially for the advanced ones. However, the sensitivity of patients to radiation varies. MicroRNAs have been widely validated to associate with this diversity and we aimed to explore the mechanism of it. Material and Methods MicroRNA microarrays were performed in A549 and PC9 cell lines, as well as their radioresistant cell lines. MiR- 1246 was selected from the differential expressing microRNAs and confirmed by RT-PCR. Colony-forming assay was done to evaluate the effect of its expression to radioresistance of lung cancer cells by down-regulating and up-regulating the miR-1246. Then cell autophagy was examined by transmission electron microscope, western blot and immunofluorescence. The potential regulatory target of miR-1246 was determined by Targetscan, following the verifying by luciferase reporter assay, target mRNA and protein expression. Results MiR-1246 was up-regulated in radioresistant A549 and PC9 cell lines than normal A549 and PC9 cell lines. The overexpression of miR-1246 resulted in the increased resistance to radiation and induction of autophagy in A549 and PC9 cell lines while the inhibition of miR-1246 resulted in the decreased resistance to radiation and

deduction of autophagy in radioresistant A549 and PC9 cell lines. mTOR was the predicted target gene of miR- 1246 and the negative correlation was established between miR-1246 and mTOR at both mRNA and protein levels. Luciferase reporter assay confirmed their interaction directly. Further study indicated that the radioresistance might root in activation of autophagy by dephosphorylation of ULK-Atg13-FIP200 complexes. Conclusion MiR-1246 decreased the sensitivity of lung cancer cells to radiation through activation of autophagy by targeting mTOR. This miRNA may be a potential therapeutic target to overcome the resistance to radiation in non-small cell lung cancer patients. PO-1058 Maintenance BEZ235 following BEZ235 and radiation prolongs therapeutic effect in colorectal cancer Y.H. Chen 1 , M.F. Wei 1 , S.H. Kuo 1 1 National Taiwan university hospital, Division of radiation oncology- department of oncology, Taipei, Taiwan Purpose or Objective Our previous study demonstrated that the administration of NVP-BEZ235 (BEZ235), a dual PI3K/mTOR inhibitor, before radiotherapy (RT) enhances the radiotherapeutic effect in colorectal cancer cell (CRC) both in vitro and in vivo. For this study, we evaluated whether maintenance BEZ235 treatment following BEZ235 and RT treatment prolongs the antitumor effect in CRC. Material and Methods K-RAS mutant CRC cells (HCT 116 and SW 620) and wild type CRC cells (HT 29) and HCT116 xenograft tumors were separated into 5 study groups: (1) untreated (control), (2) RT alone, (3)BEZ235 alone, (4)RT combined with BEZ235 (RT+BEZ), and (5) maintenance BEZ235 following RT with BEZ235 (RT+BEZ+mBEZ). The colony formation, apoptosis, mTOR signaling (p-eIF4E and p- rpS6), DNA double-strand break (DSB) repair-related molecules (p-ATM), and VEGF-A expression were assessed both in vitro and in vivo. Results RT+BEZ+mBEZ group significantly inhibited cell viability and increased apoptosis (cleaved PARP) in three CRC cells when compared with those in the RT+BEZ treatment, RT alone, BEZ alone, and untreated control groups in vitro. In HCT116 xenograft tumor model, RT+BEZ+mBEZ treatment significantly reduced the tumor size than RT+BEZ treatment, RT alone, BEZ alone and control groups. Furthermore, compared with the RT+BEZ treatment, RT alone, BEZ alone and control groups, the expression of p-eIF4E, p-rpS6, and p-ATM was significantly downregulated in the RT+BEZ+mBEZ group both in vitro and in vivo studies. The angiogenesis-related VEGF-A expression in the HCT116 xenograft tumor cells and in three CRC cells were also significantly downregulated in the RT+BEZ+mBEZ treatment group. Conclusion Maintenance BEZ235 treatment in CRC cells prolonged the inhibition of cell viability, enhancement of apoptosis, attenuation of mTOR signaling, impairment of DNA DSB Poster: Radiobiology track: Radiobiology of colorectal cancer