Abstract Book

S1278

ESTRO 37

Purpose or Objective IGF-1 and Insulin receptors (IGF-1R and IR) are increased in various cancers. Receptor stimulation leads to enhanced glucose consumption and protein synthesis and thus tumor growth through the Akt/mTOR pathway. Increased expression of IGF-1R has been linked to radioresistance, and IGF-1R is an emerging target in radiotherapy. The IGF-1R and IR inhibitor OSI-906 has shown promising results and is undergoing clinical testing. We set out to investigate if IGF-1R and IR inhibition is associated to decreased Akt/mTOR activation and glucose uptake in cancer cells, and to develop a PET detectable probe for IGF-1R and IR based on chemical OSI-906 was used to detect Insulin and IGF-1 sensitive cancer cells. Effect of inhibition was assessed with 18 F- FDG uptake, measurements of glycolysis and phosphorylations on Akt and mTOR in stimulated and non- stimulated conditions. Furthermore, we are currently assessing the specificity of [11C]-methyl-OSI-906 in tissue samples. Results Metabolic in vitro assays based on 18 F-FDG and extracellular flux analysis revealed that both insulin and IGF stimulated glucose uptake and lactic acid formation in most cell lines. These changes were effectively inhibited by OSI-906. The most pronounced effect was detected in SW948 colon cancer cells and in accordance with metabolic data, Akt and mTOR phosphorylation could be stimulated by IGF-1 and insulin, and this stimulation was effectively inhibited by OSI-906. Non- radioactive methyl-OSI-906 (backbone for the PET tracer) was able to block receptor stimulation and we are currently assessing the specificity of [11C]-methyl-OSI- 906. Conclusion Present results demonstrate that IGF-1R and IR inhibition reduce Akt/mTOR signaling, glycolysis and 18 F-FDG uptake in SW948 cells. Furthermore, [11C]-methyl-OSI-906 may detect cells responsive to IGF-1R and IR inhibition monotherapy or combination therapy with radiotherapy, which could allow for rational individualized therapy. EP-2316 Inhibiting ephrin reverts oncophenotype and radiosensitizes embryonal rhabdomyosarcoma cells. F. Marampon 1 , G.L. Gravina 1 , C. Festuccia 1 , F. De Felice 2 , D. Musio 2 , V. Tombolini 2 1 University of L'Aquila, of Biotechnological and Applied Clinical Sciences- Division of Radiation Oncology- University of L'Aquila- L'Aquila- Italy., L'Aquila, Italy 2 Unversity of Rome- Sapienza, of Radiological- Oncological and Pathological Sciences, Rome, Italy Purpose or Objective EPH (erythropoietin-producing hepatocellular) receptors are clinically relevant targets in several malignancies. This report describes the effects of GLPG1790, a new potent pan-EPH inhibitor, in human embryonal rhabdomyosarcoma (ERMS) cell lines. Material and Methods EPH-A2 and Ephrin-A1 mRNA expression was quantified by real-time PCR in 14 ERMS tumour samples and in normal skeletal muscle (NSM). GLPG1790 effects were tested in RD and TE671 cell lines, two in vitro models of ERMS, by performing flow cytometry analysis, Western blotting and immunofluorescence experiments. RNA interfering experiments were performed to assess the role of specific EPH receptors. Radiations were delivered using an x-6 MV modification of OSI-906. Material and Methods

photon linear accelerator. GLPG1790 (30 mg/kg) in vivo activity alone or in combination with irradiation (2 Gy) was determined in murine xenografts. Results Our study showed, for the first time, a significant upregulation of EPH-A2 receptor and Ephrin-A1 ligand in ERMS primary biopsies in comparison to NSM. GLPG1790 in vitro induced G1-growth arrest as demonstrated by Rb, Cyclin A and Cyclin B1 decrease, as well as by p21 and p27 increment. GLPG1790 reduced migratory capacity and clonogenic potential of ERMS cells, prevented rhabdosphere formation and downregulated CD133, CXCR4 and Nanog stem cell markers. Drug treatment committed ERMS cells towards skeletal muscle differentiation by inducing a myogenic-like phenotype and increasing MYOD1, Myogenin and MyHC levels. Furthermore, GLPG1790 significantly radiosensitized ERMS cells by impairing the DNA double-strand break repair pathway. Silencing of both EPH-A2 and EPH-B2, two receptors preferentially targeted by GLPG1790, closely matched the effects of the EPH pharmacological inhibition. GLPG1790 and radiation combined treatments reduced tumour mass by 83% in mouse TE671 xenografts. Conclusion Taken together, our data suggest that altered EPH signalling plays a key role in ERMS development and that its pharmacological inhibition might represent a potential therapeutic strategy to impair stemness and to rescue myogenic program in ERMS cells. EP-2317 The role of p21 in ionizing radiation induced premature senescence J. Wang 1 1 Institute of Modern Physics- Chinese Academy of Sciences, Biophysics, Lanzhou, China Purpose or Objective Cellular senescence can be triggered by diverse genotoxic stresses, such as telomere dysfunction, activated oncogenes, ionizing radiation and reactive oxygen species. Current investigations believe that the DNA damage response (DDR) signal, long term cell cycle arrest and activation of p53 or p16 pathway are responsible for stress-induced senescence. However, the molecular mechanisms of the long term arrested cells undergoing senescence are still unknown. Material and Methods Here we explored the molecular bases of cellular senescence by measuring senescence associated-β- galactosidase, protein expression levels and cell cycle progression in irradiated human melanoma A375 cells. Results Our results demonstrated that the DDR signal induced p21 accumulation in irradiateded cells. High levels of p21 expression led to senescent induction in A375 cells. p21 is a key factor to determine the fate of long-term G2 arrested cells. In p21-upregulated cells, high levels of p21 induced Aurora A kinase decline, which ultimately resulted in mitosis skip and senescence entry at tetraploid G1 phase. In contrast, cells without p21 expression could not induce Aurora A kinase degradation, which led to G2 arrested cells enter into M phase followed by apoptosis. Conclusion Together, we suggested that p21 upregulation coupled with Aurora A kinase decline is the key event in the process of senescence entry in G2 arrested cells. These deepening interpretation of cellular senescence following