ESTRO 36 Abstract Book

543 / 1096

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. Monceau1, C. Demarquay1, A. Accarie1, L. Moussa 1, B.
Doix1, M. Benderitter1, A. Sémont1, 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) 5.106 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.
Poster: Radiobiology track: Normal tissue radiobiology
(others)
PO-0956 Prediction of irradiated cells fate: the
necessity to revisit RBE by multi-parametric
investigations
V. Paget1, M. Ben Kacem1, M. Dos Dantos2, F.
Soysouvanh 1, M. Benadjaoud 2, A. Francois1, O. Guipaud1,
F. Milliat 1
1Institute 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
2Institute 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