ESTRO 38 Abstract book

S1195 ESTRO 38

cell response to irradiation was measured using SRB assays. The LQ model was fitted to the surviving fraction of cells at the different O 2 conditions and the α and β values estimated.

Purpose or Objective Our previous study showed that miR-454-3p decreased obviously after exposure of renal carcinoma 786-O cells to X-rays. miR-454-3p targeted to BTG1, which has long been recognized as a tumor suppressor gene, through a direct interaction with the 3′-UTR of BTG1 mRNA. Here, we try to explore the function and mechanisms of miR-454-3p in renal carcinoma cells responding to ionizing radiation and detect whether miR-454-3p contributes to the instability of genome after ionizing radiation exposure. Material and Methods The human renal carcinoma 786-O cells were exposed to 2.5 Gy of X-rays. The mRNA levels and protein levels of BTG1 were analyzed by qRT- PCR and western blotting. The radio-sensitivity was quantified by assaying the number of micronuclei in binucleated cells with a fluorescence microscope after exposure. Results We found that both the mRNA levels and protein levels of BTG1 were significantly increased at 4-8 hours in renal carcinoma 786-O cells exposed to 2.5 Gy of X-rays. The number of micronuclei increased significantly in bi- nucleated 786-O cells at 36 hours when BTG1 were down- regulated by transfection of miR-454-3p mimics, implying that BTG1 contributed to maintain the genetic integrity after exposure of 786-O cells to ionizing radiation. Conclusion Our results indicate that down-regulation of BTG1 renders tumor cells sensitive to radiation. These results support our previous report that miR-454-3p regulates cellular radio-sensitivity by targeting to BTG1. Our findings may shed light on the potential application of microRNA in tumor radiotherapy. EP-2162 Applying the Linear Quadratic Model to PC-3 cells irradiated under different O2 conditions T. McMullan 1 , J. Meehan 2,3,4 , S. Langdon 2 , D.B. McLaren 3 , S. McLaughlin 5 , W.H. Nailon 1,6 1 Edinburgh Cancer Centre, Oncology Physics, Edinburgh, United Kingdom; 2 University of Edinburgh, Institute of Genetics and Molecular Medicine, Edinburgh, United Kingdom; 3 Edinburgh Cancer Centre, Clinical Oncology, Edinburgh, United Kingdom; 4 Heriot Watt University, Institute of Sensors- Signals and Systems., Edinburgh, United Kingdom; 5 Heriot Watt University, School of Engineering and Physical Sciences, Edinburgh, United Kingdom; 6 University of Edinburgh, School of Engineering, Edinburgh, United Kingdom Purpose or Objective Prostate cancer outcome is compromised by areas of tumour hypoxia, which can be three times more radioresistant than well oxygenated areas. However, taking account of hypoxia when estimating the α/β ratio and the resulting surviving fraction of cells as a function of dose is challenging. The aim of this study was to use the linear quadratic (LQ) model to fit to cell survival data obtained from PC-3 cells irradiated under a range of different O 2 conditions. Material and Methods Human prostate cancer PC-3 cells, 100 cells in each well of a 96 well plate, were cultured and prepared under normoxic (20% O 2 ), hypoxic (0.5% O 2 ), and oxic conditions close to those in the human body (7% O 2 ). Additionally, groups of 0.5% O 2 and 7% O 2 cells were transferred to 20% O 2 conditions after irradiation (Re-Ox). Irradiation was performed 24 hours after seeding in a Faxitron RX-650 cabinet X-ray device with doses in the range 0.5 – 6 Gy. The cells were left for at least 13 days before fixation and Electronic Poster: Radiobiology track: Tumour microenvironment

Results

Figure 1 : The LQ fit to the surviving fraction of cells obtained under different O 2 conditions. The LQ fits for the single dose data are shown in Figure 1. As expected, the 20% O 2 had the lowest survival fraction up to 6 Gy. The 7% Re-Ox cells, which are closer to those found in the body, had greater cell-kill at higher doses due to the larger β component. At 6 Gy the survival fraction for the hypoxic 0.5% O 2 cells (irradiated at 0.5% O 2 and kept at 0.5% O 2 until fixation) was essentially the same as the 0.5% Re-Ox cells (irradiated at 0.5% O 2 and transferred to 20% O 2 at fixation). Interestingly, the hypoxic cells show increased resistance to irradiation at low doses up to 1 Gy with their populations increasing. However, the dose increments are not sufficient to show the low dose hyper-radiosensitivity found by other researchers. Beyond 6 Gy, the β effect of cell-kill dominates in a similar manner to the 7% O 2 curve. Overall, in the dose range studied, there is a decrease in surviving fraction with increasing O 2 conditions. The 20% O 2 has an almost linear response, which is reflected in the high α value. Table 1 : Resulting alpha/beta ratios for the different O 2 conditions.

O 2 Condition α/β Description 20% 16.5 Normoxic 0.5% 14 Hypoxic (with re-ox) 7% 1.4 Normal Prostate Conclusion

The data presented demonstrates that it is possible to obtain estimates of α and β that accounts for different levels of O 2 in the tumour microenvironment. However, it is important to take account of the impact of fractionation before considering the probability of tumour control.

Electronic Poster: Radiobiology track: Immuno- radiobiology

EP-2163 Combination therapy of microglia and radiotherapy in a rat model of spontaneous glioma Y. Suzuki 1 , N. Okonogi 2 , H. Sato 3 , T. Oike 3 , Y. Yoshimoto 3 , K. Mimura 4 , S. Noda 3 , M. Okamoto 3 , T.