ESTRO 2020 Abstract book

S1064 ESTRO 2020

signature, after progression on long-term anti-PD-1, and despite advanced age. Additional immunotherapies (e.g., epitope-based vaccination) may prolong antitumor responses and may be particularly beneficial for patients with unfavorable pretreatment tumor immune signature. PO‐1815 Radiotherapy combined to Duox1 inhibition in macrophages enhances their anti‐tumor effect L. Meziani 1 1 Institut Gustave Roussy, INSERM U1030, Villejuif, France Purpose or Objective The role of tumor-associated macrophages (TAM) in response to anticancer therapies is well defined, notably in response to radiotherapy (RT, Klug et al ., 2013). The efficacy of RT can be compromised by the occurrence of side effects in the healthy tissues surrounding the tumor by inducing a chronic oxidative stress and a chronic inflammation leading in some case to tumor development. It has been shown that reactive oxygen species (ROS) produced by NADPH oxidase (NOX) are involved in genomic instability of irradiated cells (Ameziani-El-Hassani et al ., 2015). We have previously demonstrated that chronic inflammatory response, mediated by anti-inflammatory macrophages (displaying the same activation profile as TAM) promote the development of radiation-induced tissue toxicity (Meziani et al ., 2018). These data suggest a link between NADPH oxidase and macrophage in the tissue response to radiotherapy. The role of several NOXs in macrophage response to radiotherapy, such as NOX2, has been reported (Wu et al ., 2017; Xu et al ., 2016). However, the role of DUOX1 (a dual NADPH oxidase, and a member of the NOX family) in macrophage activation and response to radiotherapy is poorly known. Material and Methods We evaluated the role of DUOX1 in macrophage activation in vitro and then we evaluated the anti-tumor effect of activated DUOX1 KO macrophages. Results We showed that DUOX1 plays a pivotal role in macrophage differentiation/activation. Interestingly, we showed that DUOX1 controls in vitro macrophage secretion of IFNγ and CCL4. Furthermore, we showed that DUOX1 is involved in macrophage phagocytosis and controls Src phosphorylation in activated macrophages. Interestingly, it has been shown that Src promotes anti-inflammatory macrophage generation (Hu et a., 2018) and plays a pro-tumoral role in several tumor models (Lamar et al., 2019). We have then evaluated the in vivo relevance of DUOX1 in macrophage activation and in the tumor response to radiotherapy. To this end, we have performed intra-tumor injection of macrophages derived from WT or Duox1 KO mice. Bone marrow derived macrophages (BMDMs) from both WT and KO mice were activated in vitro with GM-CSF to induce pro-inflammatory (anti-tumor) profile, and then injected intra-tumorally in subcutaneous MC38 tumours. Intra- tumor injection of WT BMDMs induced a limited delay in tumor growth. Interestingly, injection of Duox1 -/- BMDMs resulted significantly enhanced a significant tumor growth delay when compared with the injection of WT BMDMs. More interestingly, a 8 Gy tumor irradiation one day before BMDM injection enhanced the anti-tumor effect of injected DUOX1 KO BMDMs. This anti-tumor effect seems to be mediated by an IFNg response. Conclusion Herein, we demonstrate that inhibition of DUOX1 represents a promising approach to modulate macrophage response/polarization in order to enhance their anti- tumoral activity.

CXCL11) at time point 3 and, according to the KEGG analysis, a decrease of cell adhesion molecules (CD22, CD6) and proteins involved in NK cytotoxicity and graft vs. host reactions (KIR3DL1, FASLG, KLRD1). The variability between patients was small. (Fig. 1: CRT summary)

Conclusion We detected treatment associated differences in multiple proteins involved in the innate and adaptive immune system using a comprehensive proteomics approach. Clear differences emerged between SBRT and CRT. These results are the basis for further studies to unravel the optimal priming of the immune system by RT. PO‐1814 RT‐induced abscopal effect despite unfavorable pretreatment immune signature E. Firat 1 , T. Watanabe 1 , J. Scholber 1 , R. Luo 1 , N. Ehrat 1 , F. Meiss 2 , G. Niedermann 1 1 Uniklinik Freiburg, Dept. of Radiation Oncology, Freiburg, Germany ; 2 Uniklinik Freiburg, Dept. of Dermatology and Venerology, Freiburg, Germany Purpose or Objective Radiotherapy can elicit abscopal effects in non-irradiated metastases, particularly under immune checkpoint blockade (ICB), but clinical trials so far suggest only limited success. We report on two elderly patients with oligometastatic melanoma treated with anti-PD-1 and stereotactic body radiation therapy (SBRT). Material and Methods Pretreatment tumor material obtained a few weeks before ICB and concomittant early SBRT was analyzed by bulk whole-exome sequencing and immunohistochemistry. In addition, PBMCs were analyzed at various time points by flow cytometry. T cell responses to differentiation antigens and to neoepitopes were also characterized. Results Patient 1 had a favorable pretreatment immune signature, indicating the presence of large numbers of exhausted T cells, and immediately showed a complete response (CR), now already lasting for 4 years. Patient 2 had an unfavorable pretreatment immune signature, indicating a prevalence of immunosuppressive myeloid cells. Nonetheless, he showed a metabolically complete systemic response following a second SBRT after progression on long-term anti-PD-1 (> 10 months) and the first SBRT, i.e., a strong RT-induced abscopal effect. However, after 2.5 years, his disease progressed. Upon initiation of ICB and the subsequent first SBRT, patient 1, who rapidly developed a CR, showed a stronger increase in Ki67+ CD8+ T cells compared to the pretreatment levels than patient 2. Even during the first progression period following ICB initiation and the first ineffective SBRT, T cells specific for differentiation antigens and neoepitopes were detected in the blood of patient 2. Conclusion Our data suggest that oligometastatic patients, where a large proportion of the tumor mass can be irradiated, are good candidates to improve ICB responses by RT, even in the case of an unfavorable pretreatment immune