ESTRO 2022 - Abstract Book

S521

Abstract book

ESTRO 2022

Direct co-culturing with MSCs enhanced the GBCs’ clonogenic survival and proliferation rates after irradiation, whereas the GBCs’ metabolic activity was unaffected by MSC-conditioned medium. The number of MSCs migrating towards the tumor cells was found to be reduced after irradiation of the GBCs, indicating impaired secretion of chemoattractant cytokines by irradiated GBCs. Direct co-cultivation with MSCs attenuated radiation-induced apoptosis and caused a pronounced G2/M arrest in primary GBCs after irradiation. Furthermore, the presence of MSCs increased GAP43 expression and led to a distinct pattern of GAP43 localization in primary GBCs. SiRNA-based knock-down of GAP43 resulted in a reduction of clonogenic survival of irradiated GBCs both in mono- and co-culture. Conclusion Bone-marrow derived MCSs increase the radioresistance of GBCs, potentially contributing to the tumor-protective effects of tumor-infiltrating MSCs in GBM patients. MSC-mediated up-regulation of GAP43 in GBCs is suggested as a potential molecular mechanism underlying the observed radioprotection of GBCs in the presence of MSCs. C. Fjeldbo 1 , C.H. Julin 2 , M. Jonsson 2 , E. Aarnes 2 , T. Hompland 2,3 , T. Hillestad 3 , V.E. Skingen 2 , A. Nilsen 2 , U.B. Salberg 2 , A.K. Lie 4 , G.B. Kristensen 5,6 , H. Lyng 2,7 1 Oslo University Hospital, Department of Radiation Biology, Oslo, Norway; 2 Oslo University Hospital, Department of Radiation Biology , Oslo, Norway; 3 Oslo University Hospital, Department of Core Facilities, Oslo, Norway; 4 Oslo University Hospital, Department of Pathology, Oslo, Norway; 5 Oslo University Hospital, Department of Gynecological Oncology, Oslo, Norway; 6 Oslo University Hospital, Institute of Cancer Genetics and Informatics, Oslo, Norway; 7 University of Oslo, Department of Physics, Oslo, Norway Purpose or Objective Cancer cells are exposed to metabolic stress caused by hypoxia, lactate and acidic pH in the tumor microenvironment. Adaptation to these metabolic stress conditions is required for the cells to survive. A better understanding of the stress responses can lead to new therapeutic strategies and be of clinical importance. We here aimed to determine regulatory networks of transcription factors (TFs) and their target genes in the response to hypoxia (HYP), lactic acidosis (LA) and hypoxia combined with lactic acidosis (HYP-LA) in cervical cancer, and further to identify biological features associated with each response. Materials and Methods The regulatory networks were constructed using Illumina gene expression data from HeLa and SiHa cells exposed to each stress condition, and from tumour biopsies of 280 patients with locally advanced cervical cancer. HYP, LA and HYP-LA metagenes were determined in clinical gene expression data, based on correlations with cell line derived seed genes. iRegulon was used to detect enriched TF motifs in each metagene and construct the regulatory network of each stress response. Biological associations were identified by gene set enrichment analyses of the TF target genes and genes correlating with calculated target gene scores. Stroma fraction in tumor biopsies, hypoxia level images from DCE-MRI (n = 59), small RNA sequencing data for miR-200 (n = 200), a well-known inhibitor of epithelial-mesenchymal transition (EMT), and immunohistochemistry data for HIF1A (n = 261), T-cells (CD8) (n = 260), vascularization (Factor VIII) (n = 247), and EMT (Vimentin) (n = 23) were used to validate gene expression-based findings. TCGA data (n=252) were used for validation in an external cohort. Results Significant differences in the regulatory networks were found among the three stress responses. HIF and AP-1 were identified as important TFs for the HYP response. Upregulation of TCF12 and downregulation of SMAD4 was among the most important TFs for LA and HYP-LA, respectively. The HYP response was associated with high expression of glycolysis genes and downregulation of anti-tumor immunity. For the LA response, positive associations with EMT, stroma fraction and vascularization were identified. HYP-LA was associated with severe hypoxia by imaging, upregulation of genes involved in cytoskeleton organization and autophagy, and downregulation of oxidative phosphorylation genes. Gene sets of immunity in the HYP response and EMT in the LA response were associated with aggressive disease. Conclusion TFs, target genes and biological features differ considerably among the three stress responses in cervical cancer. Immune and stroma cells seem to be important in the aggressive tumor phenotype associated with the responses to hypoxia and lactic acidosis, respectively. OC-0596 Gene regulatory networks of metabolic stress responses in cervical cancer

OC-0597 Fractionated radiotherapy and its effect on the tumour microenvironment: a small animal study.

R. D'Alonzo 1,2,3 , S. Keam 4,2,3 , K. MacKinnon 1,2 , A. Cook 2,3,5 , A. Nowak 2,3,4 , S. Gill 6 , P. Rowshanfarzad 1 , M. Ebert 1,7,8

1 University of Western Australia, School of Physics, Mathematics and Computing, Perth, Australia; 2 University of Western Australia, National Centre for Asbestos Related Diseases, Perth, Australia; 3 Institute for Respiratory Health, Institute for Respiratory Health, Perth, Australia; 4 University of Western Australia, Medical School, Perth, Australia; 5 University of Western Australia, School of Biomedical Sciences, Perth, Australia; 6 Sir Charles Gairdner Hospital, Department of Radiation Oncology, Perth, Australia; 7 Sir Charles Gairdner Hospital, Australia, Department of Radiation Oncology, Perth, Australia; 8 5D Clinics, 5D Clinics, Perth, Australia