Abstract Book

S1281

ESTRO 37

TMZ show later recurrences and improved survival. This might be explained by the fact that proneural subtype of GBM who did not undergo a phenotype shift to other subtype during treatment has a better prognosis. Further research is needed to determine whether this could have an impact on future management of GBM therapy. EP-2322 The radiosensitizing effect of Nanodiamonds (NDs) on HeLa cells under X-ray irradiation H. Wang 1 , X. Chen 2 , H. Wang 2 1 Peking University Third Hospital, Radiation Oncology, Beijing, China 2 School of Pharmaceutical Sciences- Peking University, Department of Chemical Biology, Beijing, China Purpose or Objective To investigate biological effects of nanodiamonds (NDs), a very attractive nanoparticle of their superior chemical stability, biocompatibility and drugs accommodating ability, combined with conventional radiotherapy. Material and Methods The HeLa cells were maintained in DMEM contained FBS, penicillin and streptomycin. The size distribution and zeta potentials were determined in distilled water, PBS and DMEM with a zeta-potential analyzer. Qualitative analysis of the cellular uptake of NDs was performed by Raman microscopy. The cells got the vehicle control DMEM or NDs for 24 h before irradiation after allowing cells time to attach overnight. Hela Cells were irradiated immediately after being exposed to NDs in a 6MV X-ray medical linear accelerator at 400 MU/min at dose of 0, 4, 8, and 16Gy. The CCK-8 assays were performed to assess radiosensitizing effect of 100µg/ml NDs in different dose of radiation (0, 4, 8, and 16Gy), and various concentrations (6.25, 25, 100 and 200µg/ml) diluted to in 1× DMEM with the irradiation dose of 4Gy. Clonogenic survival assay were performed to assess the radiosensitizing effect of NDs on HeLa cells under different doses of irradiation (0, 4, 8, and 16Gy), and various concentrations (0, 6.25, 25, 100 and 200µg/ml) of NDs. Student’s t-test was used to reveal statistical differences between groups. P<0.05 was considered statistically significant. Results Many irradiated cells were changed, from epithelial to oval. When the dose of radiation was raised from 4Gy to 16Gy, the images showed the number of attached cells was also decreased. The combined exposure of NDs (100µg/ml) and irradiation (4 Gy and 8Gy) significantly decreased the rate of cell viability in Hela cell line as compared to each single exposure (NDs or irradiation alone). Clonogenic survival images showed that the number of colonies decreased with the increasing in the radiation dose. The survival curves of Hela cells in the presence of NDs (100µg/ml) irradiated with X-rays suggested clearly that the cell survival fraction decreased along with the increasing in the radiation dose after normalizing for the cytotoxicity induced by NDs alone. The survival curves of Hela cells also showed that survival fraction of Hela cells in the presence of NDs (100µg/ml and 200µg/ml) decreased under 4 Gy radiation after normalizing for the cytotoxicity induced by NDs alone. Conclusion In summary, our findings show for the first time that NDs enhanced the radiosensitivity of Hela cells in vitro. The combined exposure 100µg/ml NDs and 4Gy radiation decreased the rate of cell viability in Hela cell line as compared to single exposure (NDs alone). These results show that NDs might be modified as radiation sensitizer

for biomedical applications. Furthermore, they could be designed as the carriers with radiosensitivity, loading other radiation sensitizers or drugs for the combination of chemotherapy and radiation therapy. EP-2323 Effects of the proteasome inhibitor bortezomib on radiosensitivity of glioblastoma cells C. Forster 1 , D. Schilling 1,2 , M. Wank 2 , T.E. Schmid 1,2 , S.E. Combs 1,2 1 Department of Radiation Oncology, Klinikum rechts der Isar- Technische Universität München, Munich, Germany 2 Institute of Innovative Radiotherapy iRT, Department of Radiation Sciences DRS- Helmholtz Zentrum München, Munich, Germany Purpose or Objective Glioblastoma multiforme is the most common and most aggressive primary brain tumor in adults. Standard treatment of this WHO grade IV tumor consists of surgical resection followed by chemotherapy with temozolomide and radiotherapy. But still, median overall survival is only about 15 months. One reason for this poor prognosis is the occurrence of radioresistance that limits the efficacy of radiotherapy. Therefore, new therapies that render glioblastoma more susceptible to radiation are urgently needed. Bortezomib (PS-341, Velcade), a cytostatic drug used in the treatment of multiple myeloma, inhibits the 26S proteasome highly selective and reversible. Radiosensitization by bortezomib has already been shown in other tumor entities. So the aim of this study was to investigate radioresponsiveness of glioblastoma cells after treatment with bortezomib. Material and Methods Cell cycle analysis was performed with the glioblastoma cell line LN18. Cells were treated with bortezomib (0, 5, 10, 20, 40nM) and fixed after different time points (4, 8, 12, 16, 24, 48h). After cell cycle staining and FACS analysis, cell cycle distribution was analyzed with ModFit (Verity Software House). To investigate clonogenic survival of GBM cells, colony forming assays were performed. LN18 cells were treated with 20nM bortezomib for 24h. Then they were irradiated using different 200kV x-ray doses (1, 2, 4, 6, 8Gy) at the RS225A irradiation device (Gulmay Medical Ltd.). Cells were fixed and stained 12 days after plating. The colony counter GelCount (Oxford Optronix) was used to determine the number of colonies. Results As the cell cycle phase is significantly involved in mediating radioresistance, first the effect of bortezomib on cell cycle arrest was investigated. Bortezomib leads to a time and concentration dependent arrest in the G 2 M- phase. Significant effects start at concentrations of 20nM and incubation time of 8h. Maximum changes are observed after 16-24h. The regression of G 2 M arrest after 48h may result from the half-life (40-193h) of bortezomib and its reversible inhibitory potential. Due to the results from cell cycle analysis, LN18 cells were treated with 20nM bortezomib for 24h, irradiated and the clonogenic survival then analyzed. Preliminary data indicate that bortezomib increases radiosensitivity of LN18 cells. Conclusion Bortezomib effectively arrests LN18 cells in G 2 M-phase, which is known to be the most radiosensitive phase. Preliminary experiments reveal the radiosensitizing potential of bortezomib. Further cell survival studies with other treatment schedules and different GBM cell lines