ESTRO 36 Abstract Book

S528 ESTRO 36 _______________________________________________________________________________________________

Material and Methods Adult male C57/BL6 mice placed in a silicone mold were exposed to rectal irradiation using a linear accelerator (Varian Clinac 600 CD), the field limited to 1,5 cm of the distal part of the colon. Each mouse received 6 or 8 Gy, twice daily in 12 hours intervals, in 2, 3 or 4 fractions total. Acute cell apoptosis was examined, and histological changes at six weeks post-irradiation. Results Irradiation caused apoptosis at 4.5 hours, mainly limited to the distal colon. At six weeks post-irradiation, crypts displayed overt signs of radiation-induced degeneration, as has been described in human irradiated intestinal tissue. The number of degenerated crypts was heavily increased at the fourth fraction, regardless of dose. The number of macrophages, indicating inflammation, was likewise apparent after the fourth fraction. Crypt damage was restricted to individual crypts, nearby crypts were unaffected with regards to cell production and survival. Angiogenesis was induced, likely as a compensatory mechanism for hypoxia. Conclusion Our model is suitable to study late gastrointestinal injury induced by high-dose fractionated radiation. The placement of the radiation field makes the model especially convenient for testing interventions that can be delivered rectally. PO-0955 Co-treatment of MSC and vascular permeability inhibitor reduces radiation side effects on the colon V. Monceau 1 , C. Demarquay 1 , A. Accarie 1 , L. Moussa 1 , B. Doix 1 , M. Benderitter 1 , A. Sémont 1 , N. Mathieu 1 1 Institut de Radioprotection et de Sûreté Nucléaire IRSN, PRP-HOM- SRBE- LR2I, Fontenay aux roses, France Purpose or Objective The efficacy of radiotherapy requires an optimal compromise between tumor control and normal tissue injury. Non-neoplastic tissues around abdomino-pelvic tumor can be damaged by ionizing radiation leading to acute and/or chronic gastrointestinal complications which affect quality of life with substantial morbidity and mortality. There is no unified approach to the assessment and the treatment of radiotherapy delayed side effects, characterized mainly by uncontrolled inflammation and tissue fibrosis. We previously demonstrated that mesenchymal stromal cells (MSC) treatment improves colonic regeneration and reduces partially the ulcer size by the margins (Sémont, 2013). Moreover, studies showed that the vascular compartment is improved after MSC treatment and could play a key role in the inflammatory process and the epithelial regeneration. However, these aspects have not yet been investigated after irradiation. In this study, we investigate the effect of MSC treatment on vascular compartment. We analyze the angiogenesis process, progenitor’s recruitment in blood and associated chemoattractant molecules secretion as well as vascular permeability. The aim of this study is to determine a new way to improve MSC treatment. Material and Methods We generated, in SD rat, colonic radiation-induced lesions similar of those seen in patients suffering of late side effects after pelvic radiotherapy (29Gy). Three weeks after irradiation (established damages) 5.10 6 of MSC from fat tissue were injected intravenously (IV). Results The first results showed that MSC treatment increase the amount of blood vessels. This process is associated with an increase of the growth factor VEGF, but also a recruitment of endothelial progenitor cells, two events necessary for the neo-vascularization. We also demonstrated that MSC treatment ameliorates the quality of blood vessels (the number of fully muscularized capillaries was reduced in ulcer and border areas).

However, MSC treatment has no effect on the vascular permeability nor the number of inflammatory cells. Therefore, we realized MSC injections concomitantly with an inhibitor of vascular permeability which was iteratively infused intravenously. We demonstrated that the co- treatment reduces considerably the size of the ulcer comparatively with only MSC treatment suggesting that the beneficial effects of MSC were potentiated with an inhibitor of vascular permeability. Conclusion Results of this study constitute a first approach to demonstrate the therapeutic benefit of MSC infusion on vascular compartment in a model of severe colonic damages induced by radiations. We also characterized the molecular mechanisms involved in regenerative capacities of MSC and determined that the limitation of the vascular permeability could be a way of therapeutic improvement. This cell and pharmacologic co-treatment could be used for compassionate applications to reduce colorectal damages induced by pelvic radiotherapy. PO-0956 Prediction of irradiated cells fate: the necessity to revisit RBE by multi-parametric investigations V. Paget 1 , M. Ben Kacem 1 , M. Dos Dantos 2 , F. Soysouvanh 1 , M. Benadjaoud 2 , A. Francois 1 , O. Guipaud 1 , F. Milliat 1 1 Institute for Radiological Protection and Nuclear Safety IRSN, Department of Radiobiology and Epidemiology SRBE / Research on Radiobiology and Radiopathology Laboratory L3R, Fontenay-aux-Roses- Paris, France 2 Institute for Radiological Protection and Nuclear Safety IRSN, Department of Radiobiology and Epidemiology SRBE, Fontenay-aux-Roses- Paris, France Purpose or Objective The evaluation of radiosensitivity is historically linked to the survival fraction measured by the clonogenic assay, which is until now the gold standard in such evaluation. The representation of the survival fraction as a function of the dose leads to survival curves which are modelled by the linear-quadratic model (LQ-model). The Relative Biological Effectiveness (RBE) is defined as the ratio of the doses required by two types of ionizing radiations to cause the same biological effect (for instance the survival fraction). The RBE is an empirical value that varies depending on the type of particle, the Linear Energy Transfer (LET), the dose rate and the dose fractionation, and can be easily used to predict biological outcome in different situations. Nevertheless, the clonogenic assay is a quite restrictive method which does not take into account cell-cell interactions and the phenotype of surviving cells as well. Thus, the aim of this study is to demonstrate, by a proof of concept, the limits of the clonogenic assay to predict the cellular fate and in a lesser extend its unsuitability to predict accurately on healthy tissues the risk associated to the use of ionizing radiations. Material and Methods Radiation-induced damage to the vascular endothelium is potentially involved in the initiation and the development of normal tissue injury. Thus, in this study we compared the biological effects on HUVECs (Human Umbilical Vein Endothelial Cells) exposed to low energy x-rays (generated at 220 kV on a SARRP) and high energy x-rays (generated at 4 MV on a LINAC). Cell survival fractions were measured/calculated by using clonogenic assay while morphological changes, cell viability/mortality, cell cycle analysis and β-galactosidase activity were evaluated by flow cytometry. Finally molecular footprinting of 44 genes Poster: Radiobiology track: Normal tissue radiobiology (others)