ESTRO 36 Abstract Book

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S540 ESTRO 36
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'radiation/hypoxia induced abscopal effects” offer one
more possibility for the oligometastatic population also to
get cured. We continue to investigate this hypothesis in
the laboratory and clinical setting.
Poster: Radiobiology track: Radiobiology of colorectal
cancer
PO-0976 Mechanisms of normal tissue t oxicity from
SAHA, an HDAC inhibitor and radiosens itizer
I.S. Barua1,2, A.H. Ree1,2 , L. Sønstevold1, K.R . Redalen 1,
E. Kala nxhi1
1 Akershus University Hospital- Norway, Dep artment of
Oncology, Oslo, Norway
2 Institute of Clinical Medicine- University of Oslo,
Campus AHUS, Oslo, Norway
Purpose or Objective
Histone deacetylase inhibitors (HDACi) are therapeutic
agents, which through epigenetic alterations can cause
tumor cell death and have shown radiosensitizing
properties in preclinical models. HDACi have been largely
regarded as tumor-specific, while their effects on normal
tissues remain poorly investigated. The latter is important
as an increase in therapeutic efficacy resulting from
combining such agents with radiotherapy may come at the
expense of patient tolerance, undesired treatment
interruptions and dose limitations. In the phase I Pelvic
Radiation and Vorinostat (PRAVO) study, we investigated
mechanisms of adverse effects to the HDACi vorinostat
(suberoylanilide hydroxamic acid; SAHA) when given as
potential radiosensitizer. Vorinostat-induced
transcriptional responses in patients’ peripheral blood
mononuclear cells implicated cell death pathways as a
possible mechanism of toxicity. In experimental models
we showed that apoptosis in epithelial cells of the
intestinal mucosa may account for the gastrointestinal-
related adverse effects commonly associated with the use
of HDACi (Kalanxhi E, et al. Cancer Res Treat, 2016). In
the current work we further investigate HDACi-induced
apoptosis and the possible interplay with autophagy in
experimental normal and colorectal cancer (CRC) models.
Material and Methods
Two normal cell lines (rat IEC-6 intestinal epithelial cells,
human BJ fibroblasts) and two CRC cell lines (HCT116,
HT29) were exposed to a therapeutically relevant
concentration of SAHA alone, or in combination with the
caspase inhibitor ZVAD-fmk and the autophagy inhibitor
bafilomycin A1 for 24 hours. Induction of apoptosis and
autophagy were analyzed with flow cytometry (Annexin
V/PI staining) and western blot analysis (LC3 I/II and p62
expression).
Results
SAHA induced apoptosis in the CRC cell lines with 42% and
26% of the HCT116 and HT29 cell populations respectively,
showing Annexin V/PI staining indicative of early and late
phases of apoptosis (Figure 1). Normal BJ fibroblasts
remained unaffected, whereas intriguingly, intestinal
epithelial IEC-6 cells responded similarly as the cancer
cells, although apoptosis was induced at a lesser extent
(18% of cells). Addition of ZVAD-fmk halved the number of
apoptotic cells in CRC cells, whereas the same number of
IEC-6 cells (16%) displayed apoptotic phenotypes. We
further looked into induction of autophagy and found that
SAHA induced autophagy both in the CRC cell lines and the
IEC-6 cells, as reflected by increased levels of the
autophagy protein LC3-II and decreased levels of p62.
Conclusion
Treatment with the HDACi SAHA resulted in induction of
apoptosis and autophagy in both CRC cells and at a lesser
extent in a relevant normal tissue model. Firstly, our
results may contribute to explain adverse effects of SAHA
on normal intestinal epithelial cells, and secondly,
identify a therapeutic window where tumor
radiosensitization can be achieved by SAHA.
PO-0977 Plasma lipidomics for predictive biomarker
analysis in rectal cancer.
P. Bulens 1,2, A. Debucquoy2, K. Bloch 2, S. Fieuws2, J.
Swinnen2, K. Haustermans1,2
1University Hospital Leuven, Radiation Oncology, Leuven,
Belgium
2KU Leuven - University of Leuven, Oncology, Leuven,
Belgium
Purpose or Objective
Selection of patients with locally advanced rectal cancer,
eligible for individualized treatment strategies, is
hampered by the lack of reliable predictors of response.
Plasma markers based on liquid biopsies would allow
minimally invasive patient stratification. Most liquid
biopsy approaches are based on the detection of free
circulating DNA or tumor cells. Since the development and
progression of cancer is associated with dramatic changes
in lipid metabolism, we propose a radically different
approach based on alterations in circulating lipids.
Material and Methods
From prospectively collected plasma samples of 85 rectal
cancer patients at 3 time points (before chemoradiation
(CRT), 2 weeks into CRT, end of CRT), lipids were
extracted using a modified Bligh-Dyer protocol. Samples
were subjected to mass spectrometry-based lipid profiling
on a fully operational lipidomics platform. This approach
allowed us to assess the concentration of approximately
200 different lipid species including phosphatidylcholine
(PC), phosphatidylethanolamines (PE),
phosphatidylinositol (PI), phosphatidylserine (PS) and
ceramides (Cer). Based on the assessment of these
species, discriminative lipid profiles of patients achieving
a pathologic complete response (pCR) and patients lacking
such response will be delineated using biostatistical
approaches including PCA analysis followed by LDA and
correction for false discovery due to multiple testing.
Results
13 out of 85 patients achieved a pCR (15,3%). Preliminary
analyses showed slightly less lipogenic profiles for patients