ESTRO 38 Abstract book

S602 ESTRO 38

impact of PI3K pathway inhibition by the dual inhibitor BEZ235 on radiation sensitization of HPV pos and HPV neg HNSCC cell lines. Material and Methods The effect of BEZ235 in combination with radiation was determined for five HPV pos and five HPV neg HNSCC cell lines. Therefore, assays were used to identify alterations in the PI3K pathway and the DNA damage response (DDR), specifically ATM and DNA PKcs by Western Blot. Flow cytometric analysis was used to examine the cell cycle by Nicoletti staining and apoptosis by AnnexinV-staining. Repair of DNA double strand breaks (DSB) was visualised by gamma-H2AX foci formation and repair efficiency of homologous recombination (HR) and non-homologous end joining (NHEJ) was examined with repair plasmids. Survival after treatment was determined by colony formation assay. Results Treatment of cells with BEZ235 (50 nM) suppressed activation of Akt via Ser473 phosphorylation. Single use of BEZ235 does not interfere with cell cycle progression. In combination with irradiation, BEZ235 induces a significant increase in G1 arrest with a similar effect for both HPV pos and neg cell lines. Radiation-induced apoptosis was unaffected after the dual treatment. However, for all HNSCC cell lines DNA DSB repair was notably impaired in a way which is independently from HPV- or Akt- status but restricted to G1 cells, while clearly less effects were seen for S or G2 phase cells. These results suggest an inhibition of NHEJ, but not HR, which could be validated using repair-specific plasmids. The reduction of NHEJ could be attributed to a strong inhibition of DNA PKcs at S2056. In accordance with these data, colony formation assay revealed a significant increase of cellular radiosensitivity, which was especially pronounced for G1-phase cells. Conclusion The dual PI3K-inhibitor BEZ235 can be used to increase the radiation response of HNSCC independently from HPV- and Akt-status. PO-1084 Poly ADP-ribose polymerase-1 inhibitors enhance soft tissue sarcoma radiosensitivity: in vivo study. M. Mangoni 1,2 , M. Sottili 1 , G. Salvatore 1 , D. Pezzulla 1 , S. Lucidi 1 , M.A. Teriaca 1 , V. Maragna 1 , A. Peruzzi 1 , M. Perna 1 , G. Stocchi 1 , F. Terziani 1 , G. Caramia 1 , R. Grassi 1 , C. Talamonti 3 , G. Beltrami 4 , D. Campanacci 4 , D. Greto 1 , L. Livi 1 1 University of Florence, Radiotherapy Unit, Firenze, Italy ; 2 Istituto Toscano Tumori, Itt, Florence, Italy ; 3 University of Florence, Medical Physics Unit, Firenze, Italy ; 4 University of Florence, Orthopedic Oncology Unit, Firenze, Italy Purpose or Objective Soft-tissue sarcomas (STS) are aggressive tumors with a poor prognosis and limited effective therapeutic options, thus there is a major clinical need for novel strategies. Poly-ADP ribose polymerase (PARP)-1 promotes base excision repair and DNA strand break repair. Inhibitors of PARP (PARPi) have shown to enhance the cytotoxic effect of irradiation, and evidences suggest that PARPi could be used to selectively kill cancers defective in DNA repair. Tumorigenesis in sarcomas is linked to aberrant biological pathways and some STS have defect in DNA repair systems, so there is a rationale for using PARPi in STS. We previously demonstrated that PARPi are potent radiosensitizers on human STS in vitro models: they reduced cell survival, inhibited DNA damage repair and pro-survival ERK signaling when used in combination with irradiation. The aim of the present study was to investigate the effect of PARP inhibition and irradiation on tumorigenesis ofirradiated tumor cells in a xenograft model of rhabdomyosarcoma in mice.

Material and Methods Rhabdomyosarcoma cells were irradiated with 3 Gy, with or without a 24 hours olaparib (1 µM) pre-treatment. Non- irradiated cells were used as controls. Four group of mice were compared:1) control; 2)olaparib; 3)irradiation; 4)irradiation+olaparib. Rhabdomyosarcoma xenograft was obtained by s.c. injection of 6×10 6 cells in the flank of CD1 nude mice. Tumor volume was measured twice a week for 30 days by the formula [lenght x(width x width)]/2. Immunofluorescence and western blotting analysis have been performed. Results Olaparib alone reduced tumor growth compared to control, but without reaching a statistical significance. Irradiation alone showed an effect on tumorigenesis with a significant reduction of tumor volume compared to control. The association of olaparib and irradiation showed an even higher decrease in tumor volume compared to irradiation alone, reaching the statistical significance vs. irradiation or olaparib alone after 8 days. The mean immunofluorescence of gamma H2AX on rhabdomyosarcoma cells was significantly increased after treatment with olaparib and with radiation alone; a significantly higher intensity of fluorescence was obtained with combined treatment. Tumor growth was inversely proportional to the mean immunofluorescence of gamma H2AX. Further biomolecular analysis are ongoing. Conclusion In this study we confirmed previous in vitro data and showed that olaparib enhances the therapeutic effect of radiation on rhabdomyosarcoma xenograft, with significant reduction of tumorigenesis. These preliminary data encourage to further study association of PARPi with IR as a promising treatment for STS. PO-1085 Prolonged trifluridine/tipiracil treatment radiosensitises colorectal cancer cells K. Rothkamm 1 , T. Rieckmann 2 , S. Christiansen 1 , A. Brinker 1 , A. Stein 3 , U. Schumacher 4 , T. Frenzel 5 , C. Petersen 6 , S. Burdak-Rothkamm 6 1 University Medical Center Hamburg - Eppendorf UKE, Department of Radiotherapy and Radio-Oncology / Laboratory of Radiobiology & Experimental Radiation Oncology, Hamburg, Germany ; 2 University Medical Center Hamburg - Eppendorf UKE, Department of Otorhinolaryngology- Head and Neck Surgery / Laboratory of Radiobiology & Experimental Radiation Oncology, Hamburg, Germany ; 3 University Medical Center Hamburg - Eppendorf UKE, Department of Oncology- Hematology and Bone Marrow Transplantation, Hamburg, Germany ; 4 University Medical Center Hamburg - Eppendorf UKE, Institute of Anatomy and Experimental Morphology, Hamburg, Germany ; 5 University Medical Center Hamburg - Eppendorf UKE, Department of Radiotherapy and Radio- Oncology / Institute of Anatomy and Experimental Morphology, Hamburg, Germany ; 6 University Medical Center Hamburg - Eppendorf UKE, Department of Radiotherapy and Radio-Oncology, Hamburg, Germany Purpose or Objective Trifluridine/ Tipiracil (TFTD) has shown clinically relevant activity in colorectal cancer after fluoropyrimidine failure and may be of increased efficacy in combination with radiotherapy (RT) compared to current standard capecitabine chemoradiotherapy (RChT). As the underlying molecular mechanisms are still poorly understood, we aimed to determine the response of four colorectal cancer cell lines to TFTD alone and in combination with RT in order to provide a preclinical rationale for TFTD-based RChT treatment of rectal cancer. Material and Methods HT29 (MSS, CIN+, Ras wt, BRAF mut (V600E), p53 mut), HCT116 (MSI, CIN-, Ras mut, BRAF wt, p53 wt), SW48 (MSI,