Page 310 - 2014 Printable Abstract Book
P. 310
and attributed to an anti-angiogenic action of mTOR inhibition. Our data is consistent with a separate and
complementary explanation for radiosensitization by mTOR, that mTOR generates damaging ROS which
are distinct from radiation-induced ROS. Consequently, when damaging ROS mediated through mTOR
inhibition is combined with the damaging ROS produced by radiation. The effect is more than additive.
1
(PS5-41) Targeting DNA repair in HPV/p16-positive head and neck cancers. Ruveyda Dok ; Evert Jan Van
1;2
1
1
1
1
Limbergen ; Peter Kalev ; Esther Hauben ; Anna Sablina ; and Sandra Nuyts , University of Leuven,
2
1
Leuven, Belgium and Dana-Farber Cancer Institute, Boston, MA
Purpose: Recent evidence identifies Human Papillomavirus (HPV) related Head and Neck
carcinomas (HNSCC) as a separate subgroup of HNSCC with an enhanced response to chemo-radiation.
Recently, we showed that p16 contributes to the DNA damage response by impairing the homologous
recombination-mediated (HR) repair in HPV-positive HNSCC. This opens an opportunity to use small
molecular inhibitors like Poly-ADP ribose polymerase (PARP) inhibitors, which are known to be effective
in HR deficient tumors, in combination with ionizing radiation as a novel therapeutic strategy. We
investigated the efficacy and the molecular mechanism of the inhibitor more specifically the interaction
between p16, PARP inhibition and DNA repair. Material and methods: The DNA damage response of HPV+
(SCC154, SCC090) and HPV- (SQD9, CAL27, SC263) HNSCC cells treated with a combination of PARP
inhibitor and ionizing radiation was analyzed by clonogenic/survival assays, DNA repair assays and cell
cycle analysis. Also the influence of p16 on the combination treatment was assessed by depletion of p16
with specific siRNAs or lentiviral shRNAs in the HPV+ cells. The efficacy of the combination treatment and
relation to p16 was also assessed on protein level by immunoblotting. Results: We showed that depletion
of p16 in HPV+ cells decreased the radiation sensitivity and reduced the RAD51 foci formation, which
confirms that the radiation sensitivity depends on p16 expression levels. On top, HPV+ cells with p16
depletion formed more gH2AX foci compared to their control. Furthermore, PARP inhibition resulted in
more colonies and showed a higher survival in p16 depleted cells compared to cells expressing elevated
levels of p16. The addition of ionizing radiation resulted in an increased cytotoxicity of PARP inhibition in
HPV/p16+ cells. Further research unraveling the relation between p16, PARP inhibition and DNA repair
pathways on molecular levels is currently ongoing and will be presented at the time of the meeting.
Conclusion: These results indicate the potential use of PARP inhibitors in combination with ionizing
radiation in p16 expressing HNSCC tumors as a novel treatment strategy. However, further research
investigating the biology and the interaction between the different players is necessary.
(PS5-42) Endothelium specific HIF-1α deletion protects from radiation-induced intestinal injury. Aurore
Toullec; Valérie Buard; Emilie Rannou; Georges Tarlet; Marc Benderitter; Olivier Guipaud; Agnès François;
and Fabien Milliat, Institute for Radiological Protection and Nuclear Safety, fontenay-aux-roses, France
Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription factor composed of two
subunits HIF-1α and HIF-1β. HIF-1 α is activated by hypoxia and induces the expression of various genes
related to the adaptation of cellular metabolism to hypoxia. Interestingly, hypoxia and HIF-1α expression
level has been shown to be associated with radioresistance in malignant solid tumor, tumor recurrence
after radiation and poor prognosis. Indeed, the endothelial compartment plays a critical role in the
initiation and the progression of radiation-induced damages and HIF-1α contributes to protect intra-
308 | P a g e
complementary explanation for radiosensitization by mTOR, that mTOR generates damaging ROS which
are distinct from radiation-induced ROS. Consequently, when damaging ROS mediated through mTOR
inhibition is combined with the damaging ROS produced by radiation. The effect is more than additive.
1
(PS5-41) Targeting DNA repair in HPV/p16-positive head and neck cancers. Ruveyda Dok ; Evert Jan Van
1;2
1
1
1
1
Limbergen ; Peter Kalev ; Esther Hauben ; Anna Sablina ; and Sandra Nuyts , University of Leuven,
2
1
Leuven, Belgium and Dana-Farber Cancer Institute, Boston, MA
Purpose: Recent evidence identifies Human Papillomavirus (HPV) related Head and Neck
carcinomas (HNSCC) as a separate subgroup of HNSCC with an enhanced response to chemo-radiation.
Recently, we showed that p16 contributes to the DNA damage response by impairing the homologous
recombination-mediated (HR) repair in HPV-positive HNSCC. This opens an opportunity to use small
molecular inhibitors like Poly-ADP ribose polymerase (PARP) inhibitors, which are known to be effective
in HR deficient tumors, in combination with ionizing radiation as a novel therapeutic strategy. We
investigated the efficacy and the molecular mechanism of the inhibitor more specifically the interaction
between p16, PARP inhibition and DNA repair. Material and methods: The DNA damage response of HPV+
(SCC154, SCC090) and HPV- (SQD9, CAL27, SC263) HNSCC cells treated with a combination of PARP
inhibitor and ionizing radiation was analyzed by clonogenic/survival assays, DNA repair assays and cell
cycle analysis. Also the influence of p16 on the combination treatment was assessed by depletion of p16
with specific siRNAs or lentiviral shRNAs in the HPV+ cells. The efficacy of the combination treatment and
relation to p16 was also assessed on protein level by immunoblotting. Results: We showed that depletion
of p16 in HPV+ cells decreased the radiation sensitivity and reduced the RAD51 foci formation, which
confirms that the radiation sensitivity depends on p16 expression levels. On top, HPV+ cells with p16
depletion formed more gH2AX foci compared to their control. Furthermore, PARP inhibition resulted in
more colonies and showed a higher survival in p16 depleted cells compared to cells expressing elevated
levels of p16. The addition of ionizing radiation resulted in an increased cytotoxicity of PARP inhibition in
HPV/p16+ cells. Further research unraveling the relation between p16, PARP inhibition and DNA repair
pathways on molecular levels is currently ongoing and will be presented at the time of the meeting.
Conclusion: These results indicate the potential use of PARP inhibitors in combination with ionizing
radiation in p16 expressing HNSCC tumors as a novel treatment strategy. However, further research
investigating the biology and the interaction between the different players is necessary.
(PS5-42) Endothelium specific HIF-1α deletion protects from radiation-induced intestinal injury. Aurore
Toullec; Valérie Buard; Emilie Rannou; Georges Tarlet; Marc Benderitter; Olivier Guipaud; Agnès François;
and Fabien Milliat, Institute for Radiological Protection and Nuclear Safety, fontenay-aux-roses, France
Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription factor composed of two
subunits HIF-1α and HIF-1β. HIF-1 α is activated by hypoxia and induces the expression of various genes
related to the adaptation of cellular metabolism to hypoxia. Interestingly, hypoxia and HIF-1α expression
level has been shown to be associated with radioresistance in malignant solid tumor, tumor recurrence
after radiation and poor prognosis. Indeed, the endothelial compartment plays a critical role in the
initiation and the progression of radiation-induced damages and HIF-1α contributes to protect intra-
308 | P a g e
