ESTRO 38 Abstract book

S130 ESTRO 38

signaling pathways as a consequence of several genetic and epigenetic abnormalities. In this context, cumulative evidence supports a functional role of microRNAs, endogenous small non-coding RNA molecules that negatively regulate gene expression, in affecting radioresistance, suggesting the modulation of their expression as a novel radiosensitizing approach. In this study, we investigated for the first time the ability of miR- 205 to enhance the radiation response of prostate cancer cells. Material and Methods miR-205 reconstitution by a miRNA mimic in PCa cell lines (DU145 and PC-3) was used to elucidate miR-205 biological role. Radiation response in miRNA-reconstituted and control cells was assessed by clonogenic assay, immunofluorescence-based detection of nuclear γ-H2AX foci and comet assay. Target-protection experiments were performed by using a custom oligonucleotide designed to phisically disrupt the pairiring between the miRNA and its target PKCε. For in vivo experiments, xenografts generated by implanting DU145 cells stably expressing miR-205 in SCID mice, were exposed to 5 Gy single dose irradiation using an image-guided animal micro-irradiator (225Cx, Precision X-ray). Results Experimental data showed that reconstitution of miR-205 is able to significantly enhance the radiation response of prostate cancer cell lines and xenografts. Specifically, miR-205 exerts its radiosensitizing effect through the impairment of radiation-induced DNA damage repair, as a consequence of PKCε and ZEB1 inhibition. Indeed, phenocopy experiments based on knock-down of either PKCε and ZEB1 were able to reproduce miR-205 radiosensitizing effect, hence confirming a functional role of both targets in the process. At the molecular level, miR- 205-induced suppression of PKCε counteracted radioresistance through the impairment of EGFR nuclear translocation and consequent DNA-PK activation. Consistently, disruption of miR-205-PKCε 3’UTR pairing almost completely abrogated the radiosensitizing effect, therefore further substantiating the role of PKCε as a key effector of miRNA induced enhancement of radiation response. Conclusion Overall, our results uncovered the molecular and cellular mechanisms underlying the radiosensitizing effect of miR- 205, suggesting this miRNA as a potential positive modulator of radiation response. These findings support the clinical interest in developing a novel therapeutic approach based on miR-205 reconstitution to increase Pca sensitivity to radiotherapy. OC-0266 Pancreatic ductal adenocarcinoma sensitization to radiotherapy by bioactive food components V. Vendrely 1 , S. Amintas 2 , C. Noël 2 , I. Moranvillier 3 , I. Lamrissi 3 , B. Rousseau 2 , S. Coulibaly 4 , A. Bedel 2 , F. Moreau-Gaudry 2 , E. Buscail 5 , L. Chiche 5 , G. Belleannée 6 , C. Dupin 1 , S. Dabernat 2 1 CHU de Bordeaux, Radiotherapy, Pessac, France ; 2 Bordeaux University, Biotherapy, Bordeaux, France ; 3 Inserm 1035, Biotherapy, Bordeaux, France; 4 CHU Bordeaux, radiotherapy, Bordeaux, France ; 5 CHU de Bordeaux, Surgery, Pessac, France; 6 CHU de Bordeaux, Histopathology, Pessac, France Purpose or Objective Pancreatic ductal adenocarcinoma (PDAC) is of poor prognosis in part because of resistance to conventional treatments such as chemotherapy or radiotherapy. Some naturally occurring bioactive food components (BFCs), with pro-oxidant properties are able to potentiate the cytotoxic action of conventional drugs in the PDAC. In addition, these BFCs could increase the DNA breaks induced by ionizing radiation. Our objectives were to

Oxford Institute for Radiation Oncology, Department of Oncology, Oxford, United Kingdom Purpose or Objective Radiotherapy is an important modality in the treatment of head and neck squamous cell carcinomas (HNSCC). Patients with human papillomavirus (HPV) negative carcinomas have a poorer treatment response and prognosis than patients with HPV+ HNSCC. Therefore, it is important to develop new treatment strategies to improve treatment for HPV- HNSCC patients. p16, a tumour suppressor and cyclin dependent kinase (CDK) 4/CDK6 inhibitor, is commonly overexpressed in HPV+ HNSCC and has been linked to the high radiosensitivity of HPV+ cells. We hypothesised that blocking CDK4/CDK6 using palbociclib in HPV- HNSCC would result in radiosensitisation. Material and Methods In this study, three HPV+ and ten HPV- HNSCC cell lines were exposed to clinically relevant levels of palbociclib, combined with ionising radiation (0-8 Gy). Cell survival was measured by colony forming assays. Levels of DNA damage and recruitment of DNA damage repair factors were assessed by 53BP1/RAD51/BRCA1 foci measurement and genome instability by metaphase spreading. Cell cycle analysis was performed by propidium iodide staining and flow cytometry. Mitotic catastrophe was measured by immunofluorescent staining for a-tubulin and DAPI. Homologous recombination was measured using a GFP reporter-based system. Results A strong radiosensitising effect of palbociclib was observed in ten HPV- cell lines, whereas this did not occur in three HPV+ cell lines. This effect could also be observed in low oxygen tensions (1% O 2 ) that are commonly known to cause radioresistance. Concurrent radiation with palbociclib resulted in elevated levels of residual 53BP1 foci in HPV- UT-SCC-24A cells (figure) and high levels of chromosomal aberrations. We discovered that palbociclib reduced the expression of RAD51 and BRCA1, leading to decreased protein expression, reduced localisation to DNA damage sites, and dysfunctional homologous recombination. In addition, we showed that this repression was cell cycle independent. As a consequence of this, we observed high amounts of mitotic aberrancies which suggests that combining radiation with palbociclib leads to cytotoxicity via mitotic catastrophe. Conclusion Palbociclib caused a strong radiosensitising effect in HPV- , but not HPV+ HNSCC cell lines. Taken together, we highlight a therapeutic strategy to improve the radiosensitivity of HPV-ve HNSCC, a patient group that has an unmet and urgent need for improved radiotherapy efficacy. OC-0265 MiR-205 enhances radiation sensitivity of prostate cancer cells through PKCε and ZEB1 inhibition R. El Bezawy 1 , S. Tinelli 1 , A. Cicchetti 2 , R. Valdagni 3 , P. Gandellini 1 , N. Zaffaroni 1 1 Fondazione IRCCS Istituto Nazionale dei Tumori di Milano, Department of Applied Research and Technological Development, Milan, Italy ; 2 Fondazione IRCCS Istituto Nazionale dei Tumori di Milano, Department of Medical Physics, Milan, Italy ; 3 Fondazione IRCCS Istituto Nazionale dei Tumori di Milano, Department of Radiation Oncology 1, Milan, Italy Purpose or Objective Radiotherapy is one of the main treatment options for non-metastatic prostate cancer (PCa). Although treatment technical optimization has greatly improved local tumor control, a considerable fraction of patients still experience relapse due to development of resistance. Radioresistance is a complex and still poorly understood phenomenon involving the deregulation of a variety of