ESTRO 2020 Abstract Book

S314 ESTRO 2020

inhibits growth of a wide range of xenografts in vivo . Even though a causal relationship between tumor oxygenation and antitumor effects of CP-506 was established within one tumor model, our data demonstrate that hypoxia is not the only or even most important factor in determining its antitumor effects. Our in vitro data indeed indicate that DNA repair mutational status greatly influences the cytotoxicity of CP-506. Our findings can lead to the identification of biomarkers crucial for successful clinical implementation of CP-506. OC-0563 Hypoxia suppresses radiation-induced tumor immunogenicity in 3D breast cancer models S. Gruber 1 , M. Charpentier 2 , E. Wennerberg 2 , S. Van Nest 2 , S. Demaria 2 1 Medizinische Universität Wien, Univ.Klinik f. Strahlentherapie, Vienna, Austria ; 2 Weill Cornell Medicine, Radiation Oncology, New York, USA Purpose or Objective Immune checkpoint blockade therapy (ICB) has achieved remarkable successes in a subset of cancer patients across different malignancies, but responses are limited in breast cancer (BC), prompting investigations into combination therapies that can synergize with ICB. In pre-clinical models focal radiotherapy has been shown to induce systemic responses when combined with ICB in otherwise unresponsive tumors. Mechanistically, the DNA damage response induced by radiation is coupled with the accumulation of DNA in the cytosol of the cancer cells and leads to the production of interferon type I (IFN-I) in the tumor microenvironment (TME). IFN-I and IFN-stimulated genes (ISGs) orchestrate the recruitment and activation of immune cells. Hypoxia reduces the effects of radiotherapy and promotes an immunosuppressive TME, in part mediated by high levels of adenosine. Here we investigated the effect of hypoxia on the radiation- induced IFN-I pathway activation. Furthermore, we assessed the regulation of immuno-suppressive adenosine generating enzymes CD73 and CD38 as well as PD-L1. Material and Methods BC spheroids were generated from TSA (murine) and MDA- MB-231 (human) BC cells. 1000 cells (1T) and 40.000 cells (40T) were seeded, respectively, on day 0 and cultured for 3 days before treatment to establish non-hypoxic (1T) and hypoxic (40T) spheroids. Radiation was delivered as single doses (0 Gy, 8 Gy) or with 3 fraction of 8 Gy on 3 consecutive days. Cytosolic dsDNA was quantified fluorescence-based after subcellular fractionation (SpectraMax® Quant™ dsDNA Assay Kit). Expression of IFN- I, ISGs, PD-L1, and the adenosine generating ectonucleotidases CD73 and CD38 were assessed using RNAseq, qRT-PCR and flow cytometry. Spatial distribution and co-localization of hypoxia and proteins of interest were visualized in paraffin-embedded spheroids with immunofluorescence. Hypoxia was verified with pimonidazole-staining, yH2AX was assessed as a marker for DNA damage and Ki67 for proliferation. Results Both breast cancer models yielded comparable results. Radiation-mediated accumulation of cytosolic dsDNA induced a robust IFN-I response in 2D standard cell cultures and small, non-hypoxic spheroids. Hypoxia markedly reduced cytosolic dsDNA accumulation (p<0.001) and abolished the IFN-I response. In contrast, the radiation- induced expression of adenosine-generating enzymes CD73 and CD38 was higher in hypoxic spheroids compared to 2D and non-hypoxic spheroids. Likewise, radiation increased PD-L1 expression strongly in hypoxic spheroids.

Conclusion Our findings suggest that hypoxia is a major regulator of the ability of radiation to induce anti-tumor immune responses. We identified a twofold mechanism: hypoxia abolished the radiation-induced activation of IFN-I, and enhanced the expression of adenosine generating enzymes and PD-L1. Thus, strategies to counter hypoxia may be needed to improve the success of combinations of focal radiotherapy with ICB.

Proffered Papers: Proffered papers 28 : Gynaecology

OC-0564 Randomized trial: Surgical versus clinical staging in cervical cancer patients: Uterus-11-Trial S. Marnitz 1 , A. Tsunoda 2 , P. Martus 3 , R. Affonso 4 , V. Budach 5 , J. Sehouli 6 , H. Hertel 7 , A. Schneider 8 , A. Mustea 9 , C. Köhler 10 ; 2 Cancer Center, Gynecology, Barretos, Brazil ; 3 Biometrie, Universität Tübingen, Tübingen, Germany ; 4 Cancer Center, Radiation Oncology, Barretos, Brazil ; 5 Charité, Radiation Oncology, Berlin, Germany ; 6 Charité, Gynecology, Berlin, Germany ; 7 MHH, Gynceology, Hannover, Germany ; 8 MVZ Fürstenbergcarree, Gynäkologie, Berlin, Germany ; 9 Uni Greifswald, Gynecology, Greifswald, Germany ; 10 Asklepios, Gynecology, Hamburg, Germany Purpose or Objective FIGO stage implies a high risk of under- or overstaging of locally advanced cervical cancer. Surgical staging in cervical cancer patients has been a matter of debate since many decades. Previous studies have demonstrated significant upstaging with surgical staging. However, no randomized trial has ever shown a survival benefit when treatment concepts are modified according to surgical staging. In this abstract authors present oncologic results (PFS and OS) of a prospective, randomized multicentre trial (Uterus-11 study of the German Gynecologic Oncology Group and Radiation Oncology Group) comparing outcome of surgical staging prior to primary chemo-radiation (RCT) treatment versus imaging guided primary RCT among patients with locally advanced cervical cancer. Material and Methods Between 2009 and 2013, 255 patients with cervical cancer (FIGO IIB-IVA) were randomized to surgical staging followed by RCT (arm A) or clinical staging followed by RCT (arm B). RCT in both arms included pelvic external beam radiotherapy with weekly cisplatin at 40 mg/m 2 and brachytherapy. Extended-field radiation was performed in cases of confirmed paraaortic metastases. Primary endpoint was disease free survival (DFS), secondary overall survival (OS).