ESTRO 36 Abstract Book

213 / 1082

S200 ESTRO 36 2017
_______________________________________________________________________________________________
glutamine metabolism can be used to predict clinical
outcome of prostate cancer patients.
Conclusion
Our studies suggest that radioresistant properties of
prostate cancer cells are dynamic in nature and that
combination of irradiation with therapeutic agents which
prevent tumor cell reprogramming and metabolic switch
may restore the cytotoxic effects of irradiation in
radioresistant CSC populations.
References:
Cojoc M et al. Cancer Res. 2015; 75(7):1482-94;
Peitzsch C et al. Cancer Res. 2016; 76(9):2637-51;
Kurth I et al. Oncotarget 2015; 6(33):34494-509;
Krause M et al. Advanced Drug Delivery Reviews, 2016,
pii: S0169-409X(16)30052-7.
PV-0374 Molecular insights into a disease-relevant
DNA damage response pathway
B. Xu1
1 Southern Research Institute, Molecular Radiation
Biology Laboratory, Birmingham, USA
Purpose or Objective
The optimal DNA damage response (DDR) is critical to
prevent genetic instability. The DDR is also critical to
promote cellular survival in response to DNA damage as
targeting optimal DDR pathways leads to sensitization to
radiotherapy. The Speckle type Poz Protein (SPOP), an E3
ubiquitin ligase adaptor, has recently been identified as
the gene that has the most common somatic point
mutations in prostate cancer. SPOP mutations are
associated with genomic alterations, indicating a role for
SPOP in the maintenance of genome stability. We, and
others, have recently demonstrated a critical role of SPOP
in the DDR, suggesting SPOP mutants may represent a
subgroup of patients that have hyper sensitivity to DNA
damaging therapies. However, how SPOP mutations might
impact its function and their roles in the progress of
prostate tumorigenesis remain to be extensively studied.
The objective of this research is to elucidate the
functional significnance of SPOP in the DNA damage
response pathways and to identify a subgroup of prostate
cancer patients that have distinctive radiotherapeutic
responses.
Material and Methods
Using computational modeling, we assessed the
importance of the Serine 119 residue in the SBC-MATH
domain. We characterized prostate cancer cells
expressing the S119N dominant negative mutation using
Western blot analysis, immunofluorescence microscopy,
flow cytometry, and radiosensitivity by colony formation
analysis. We also used in situ proximity ligation assay to
demonstrate the interaction of SPOP with ATM. By mass
spectrometry we identified a list of proteins that
displayed alterations in association with SPOP in response
to DNA damage.
Results
We found that Serine 119 resideing in the SBC-MATH
binding interface is in close contact with non-polar
residue of the SPOP-binding consensus motif. We found
that prostate cancer cells expressing mutation of S119
displayed impaired DNA damage responses. Using i n situ
proximity ligation assay, we demonstrate that Serine 119
is essential for SPOP interaction with ATM. We show that
ATM phosphorylates SPOP on Serine 119 in response to DNA
damage. Characterization of the functional significance of
ATM-mediated SPOP phosphorylation indicates a wide
range of downstream targets regulating cell cycle
progression and DNA repair. By mass spectrometry we
have identified a list of proteins that displayed alterations
in association with SPOP in response to DNA damage. We
found that alterations of SPOP interaction with these
proteins are required for activation of the pathways
involved in cell cycle checkpoints and Non-Homologous
End Joining (NHEJ).
Conclusion
We reveal a critical pathway linking ATM and SPOP in
regulation of prostate cancer initiation and therapeutic
responses to radiation. This also provides the first
evidence for a pathophysiological relevant mutation
linked to ATM phosphorylation in the DDR.
Award Lecture: Jack Fowler University of Wisconsin
Award
OC-0375 Dosimetric quantification of the „true“ ano-
inguinal lymphatic drainage of anal cancer patients
H. Dapper1, G. Habl 1, M. Mayinger 1, M. Oechsner1, S.E.
Combs1, D. Habermehl1
1Klinikum rechts der Isar der Technischen Universität
München, Department of Radiation Oncology, München,
Germany
Purpose or Objective
The ano-inguinal lymphatic drainage (AILD) to the inguinal
lymph nodes is located in the subcutaneous adipose tissue
on the medial thigh. Even though those node-vessels are
very thin and hardly to detect with lymphangiography, this
fact is described and shown in standard anatomy atlases.
New fluorescence-imaging methods like the indocyanine-
green-method corroborate this fact. Anal cancer (AC)
patients undergo a combined chemoradiation (CRT)
protocol and the clinical target volume (CTV) encompasses
the inguinal lymphdrainage because of its affection in
about 30% of all patients. Current contouring atlases
suggest delineation of the primary tumor region, the
mesorectum, inguinal and iliacal lymph nodes but do not
advise the inclusion of the true AILD. Aim of this work was
the retrospective analysis of the incidental dose to the
AILD in an anal cancer patient cohort who underwent
definitive CRT with VMAT-IMRT and using structure sets
according to current guidelines.
Material and Methods
VMAT-IMRT plans of 10 anal cancer patients who had been
treated with CRT during 2014 and 2016 were analyzed. On
these plans we created a new volume, the expected ano-
inguinal lymph drain (AILD). Based on anatomic
descriptions, we connected the soft tissue between the
anus and the inguinal vessels with the following
demarcations: The caudal demarcation was defined 2 cm
below the tuberculum minus. The cranial end of AILD was
at the level of the symphysis (anal) or where no more soft
tissue connection between anus and inguinal could be
identified (inguinal). Ventral demarcation was the femoral
skin, dorsal was the transition of the gluteal muscles to
the subcutaneous adipose tissue. The lateral demarcation
was the adductor muscles (anal) and the medial femur
bone or at least 0.5 cm around femoral vessels (inguinal).
We examined dose parameters (minimum, maximum,
median, V10, V20, V30, V40, V45, V50) that were
delivered to the AILD target volume and the AILD outside
of the previous PTV (AILD-PTV) as represented in the dose-
volume histogram.
Results
All of the 10 patients received at least 39.6 Gy to the
inguinal lymph nodes, 45 Gy to the iliacal lymph nodes and
50.4 Gy to the primary tumor side. The median volume of
AILD and AILD-PTV was 1066 cm3 and 689 cm3,
respectively. Mean Dmin, Dmax and Dmean were 5.5 Gy,
58.1 Gy and 38.4 Gy for AILD and 5.5 Gy, 55.2 Gy and 31.1
Gy for AILD-PTV, respectively. Mean V30, V40, V45, V50
for AILD was 71%, 55%, 45% and 31%, respectively. For
AILD-PTV it was 57%, 29%, 18% and 5%, respectively.
Conclusion
At least 71% of the volume of the expected AILD received
at least an expected required treatment dose of 30 Gy
incidentally. Especially the caudal parts of the created
volumes, with a clear distance to the previous PTVs,