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ESTRO 36
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Figure 1.
Day fourteen clonogenic cell-survival curves for
MRT and CRT. Data are presented as mean ± SEM, n = 3,
*P < 0.05, **P < 0.01.
Conclusion
This is the first study to compare the response of DIPG cell
lines to MRT and CRT. Although MRT caused more DNA
damage that was detrimental to the cell cycle compared
to CRT, the JHH-1 cell demonstrated radio-resistance
regardless of the radiation modality used. The findings of
this study support the use of MRT as a potential alternative
to CRT for patients with radiosensitive tumours and also
contribute to our understanding of the differential
response of cancer cells to MRT and CRT.
PO-0980 MEK/ERK pathway sustains radioresistance of
embryonal
rhabdomyosarcoma
stem-like
cell
population.
F. Marampon
1
, G. Gravina
1
, C. Festuccia
1
, C. Ciccarelli
1
,
F. De Felice
2
, D. Musio
2
, V. Tombolini
2
1
University of L'Aquila, Department of Biotechnological
and Applied Clinical Sciences, L'Aquila, Italy
2
University of Rome "Sapienza", Department of
Radiotherapy, Rome, Italy
Purpose or Objective
The identification of signaling pathways that affect the
cancer stem-like phenotype may provide insights into
therapeutic targets for combating embryonal
rhabdomyosarcoma. The aim of this study was to
investigate the role of the MEK/ERK pathway in controlling
the cancer stem-like phenotype using a model of
rhabdospheres
derived
from
the
embryonal
rhabdomyosarcoma cell lines.
Material and Methods
Rhabdospheres enriched in cancer stem like cells were
obtained growing ERMS cells in non adherent condition in
stem cell medium. Stem cell markers were evaluated by
FACS analysis and immunoblotting. ERK1/2, myogenic
markers, proteins of DNA repair and bone marrow X-linked
kinase (BMX) expression were evaluated by
immunoblotting analysis. Radiation was delivered using an
x-6 MV photon linear accelerator. Xenografts were
obtained in NOD/SCID mice by subcutaneously injection of
rhabdosphere cells or cells pretreated with U0126 in stem
cell medium.
Results
MEK/ERK inhibitor U0126 dramatically prevented
rhabdosphere formation and down-regulated stem cell
markers CD133, CXCR4 and Nanog expression, but
enhanced ALDH, MAPK phospho-active p38 and
differentiative myogenic markers. By contrast, MAPK p38
inhibition accelerated rhabdosphere formation and
enhanced phospho-active ERK1/2 and Nanog expression.
ERMS cells, chronically treated with U0126 and then xeno-
transplanted in NOD/SCID mice, delayed tumor
development and reduced tumor mass when compared
with tumor induced by rhabdosphere cells. U0126
intraperitoneal administration to mice bearing
rhabdosphere-derived tumors inhibited tumor growth .
The MEK/ERK pathway role in rhabdosphere
radiosensitivity was investigated in vitro. Disassembly of
rhabdospheres was induced by both radiation or U0126,
and further enhanced by combined treatment. In U0126-
treated rhabdospheres, the expression of the stem cell
markers CD133 and CXCR4 decreased and dropped even
more markedly following combined treatment. The
expression of BMX, a negative regulator of apoptosis, also
decreased following combined treatment, which suggests
an increase in radiosensitivity of rhabdosphere cells.
Conclusion
Our results indicate that the MEK/ERK pathway plays a
prominent role in maintaining the stem-like phenotype of
ERMS cells, their survival and their innate radioresistance.
Thus, therapeutic strategies that target cancer stem cells,
which are resistant to traditional cancer therapies, may
benefit from MEK/ERK inhibition combined with
traditional radiotherapy, thereby providing a promising
therapy for embryonal rhabdomyosarcoma.
PO-0981 Disturbance of redox status enhances
radiosensitivity of hepatocellular carcinoma
H. Zhang
1
, C. Sun
1
1
Institute of Modern Physics- Chinese Academy of
Sciences, Department of Heavy Ion Radiation Biology and
Medicine, Lanzhou, China
Purpose or Objective
High constitutive expression of Nrf2 has been found in
many types of cancers, and this high level of Nrf2 also
favors resistance to drugs and radiation. Here we
investigate how isoliquiritigenin (ISL), a natural
antioxidant, inhibits the Nrf2-dependent antioxidant
pathway and enhances the radiosensitivity of HepG2 cells
and HepG2 xenografts.
Material and Methods
Treatment of HepG2 cells with ISL for 6 h, Keap1
and ubiquitination of Nrf2 were measured by RT-PCR and
Western blot. Pretreatment with ISL for 6 h followed by X-
ray irradiation, confocal microscopy was used to visualize
Nrf2 translocation to the nucleus and γ-H2AX foci. To
investigate
the
radiosensitization
effect
of
ISL, apoptosis, clonogenic potential and HepG2 xenografts
were examined.
Results
Treatment of HepG2 cells with ISL for 6 h selectively
enhanced transcription and expression of Keap1. Keap1