ESTRO 2021 Abstract Book

S194

ESTRO 2021

extracting microglial morphological parameters from different regions of the rat brain. Results

Irradiation of the 50% anterior brain sub-volume leads to a greater loss in memory function and learning than irradiation of the 50% posterior brain sub-volume, as measured by the Novel Object Recognition and Barnes maze tests. Although this difference was evident at 12 weeks after irradiation, it largely resolved at 48 weeks after irradiation. Rotarod performance was similarly impaired in all treatment groups at 12 weeks after irradiation. However, at 48 weeks after irradiation, the 50% anterior irradiated animals showed a significant improvement, while performance in the other groups declined further. Along with the differential cognitive response, we analyzed in-field and out-of-field inflammatory responses. Preliminary principal component analysis identified 6 different morphology-based microglial cell clusters in the cortex and inferior colliculus. These regions showed increased microglial activation depending on whether they were included in the radiation field. Conclusion Our data indicate that irradiation of the 50% anterior brain sub-volume leads to a greater decline in memory and spatial learning. In contrast, the 50% posterior brain sub-volume seems to be more important for locomotor function, skill and speed learning. Overall, these data suggest a regional variation in loss of neurocognitive function between the anterior and posterior parts of the brain, which might be partly mediated by region-specific microglial cell activation. OC-0286 Wnt-associated DKK3 mediates radiation-induced dermal inflammation and fibrosis L. Li 1,2,3 , R. Jennemann 4 , K. Shehzad 2 , E. Grimm 4 , R. Lopez Perez 1 , R. Sandhoff 4 , P. Nelson 2 , P. Huber 1 1 German Cancer Research Center (dkfz) and University Hospital Center, Molecular and Radiation Oncology , Heidelberg, Germany; 2 Ludwig Maximilian University of Munich, Medical Clinic and Polyclinic IV , Munich, Germany; 3 The Affiliated Hospotal of Southwest Medical University, Department of Nephrology , Luzhou, China; 4 German Cancer Research Center (dkfz), Lipid Pathobiochemistry , Heidelberg, Germany Purpose or Objective Dermal inflammation and fibrosis is a common side effect of cancer radiotherapy associated with damage to basal layer stem cells. The Dickkopf protein family is involved in the regulation of Wnt signaling. We have previously shown in renal fibrosis that Dickkopf-3 (DKK3) constitutes an immunosuppressive and profibrotic epithelial protein that acts via the Wnt pathway. Here we investigate the role of DKK3 in radiation-induced dermal inflammation and fibrosis in vitro and in vivo. Materials and Methods DKK3 global knockout C57BL/6 mice, wildtype littermate controls and Dkk3/Wnt reporter mice were irradiated with a single X-ray dose (range 20-30 Gy) to the right hind limb or the thorax, respectively. Biopsy specimens were harvested for histology (H&E, αSMA, collagen [Goldner], Ki67) and immunostaining. In vitro, specific DKK3 knockout/overexpressing immortalized human keratinocytes and dermal fibroblasts were radiobiologically characterized (clonogenic and DNA damage assays) and analyzed for their impact on DKK3 and Wnt pathway regulation in the context of the fibrotic network. Results In vivo, DKK3 -/- mice were partially protected against clinical radiation damage in terms of ulceration and hair- loss at 4 and 8 weeks after radiation, respectively. Accordingly, in skin histology, DKK3-/- mice developed less hyperplasia, showed less cell proliferation, and importantly less signs of fibrosis in terms of reduced collagen and αSMA deposition. Interestingly, however, DKK3 -/- mice showed more and not less macrophages (F4/80) and monocytes (HR3) in the skin than DKK3+/+. In vitro, irradiation of kerotinocytes increased the expression of DKK3 and activation of Wnt pathway, and DKK3 knockdown inhibited Wnt pathway activity after irradiation. In fibroblasts, overexpression of DKK3 increased the expression of TGFβ after irradiation. Conclusion Our in vitro and in vivo results indicate that Dkk3 and Wnt are regulators of radiation induced skin damage and fibrosis. The downregulation of DKK3 may reduce radiation induced skin damage and fibrosis. The attenuated fibrosis in DKK3-/- mice in terms of collagen deposition is accompanied by an increase of macrophages suggesting an antifibrotic functionality in response to radiation-induced skin damage. Together the data suggest that DKK3 might serve as a potential therapeutic target and diagnostic marker for radiation-induced skin fibrosis. OC-0287 Long-term recovery of pulmonary vasculature after thoracic irradiation requires sparing of the heart J. Wiedemann 1 , S.K. Paruchuru 1 , L.E. den Boef 1 , U. Brouwer 2 , E.M. Schouten 3 , M.G. Dickinson 3 , R.A. de Boer 3 , R.P. Coppes 4 , P. van Luijk 5 1 University Medical Center Groningen, Department of Radiation Oncology, Groningen , The Netherlands; 2 University Medical Center Groningen, Department of Cell Biology, Groningen , The Netherlands; 3 University Medical Center Groningen, Department of Cardiology, Groningen , The Netherlands; 4 University Medical Center Groningen, Department of Biomedical Sciences of Cells and System, Section Molecular Cell Biology, Groningen , The Netherlands; 5 University Medical Center Groningen, Department of Radiation Oncology , Groningen , The Netherlands Purpose or Objective When irradiating thoracic tumors, irradiation of healthy tissue of lung and heart cannot be avoided. This leads to side effects compromising quality of life and treatment efficacy. In a rat model of lung irradiation, pulmonary vascular damage plays a crucial role in the development of reduced respiratory function at 8 weeks after irradiation. This effect was more severe if cardiac diastolic function was reduced by co-irradiation of the heart. In the present study we use this established rat model to test the hypothesis whether co-irradiation of the heart has a persistent impact on the pulmonary vasculature.